Developments on the Colorado River: A Crash-Course

Blake Boles
23 min readApr 22, 2021


In Spring 2021, I road-tripped the Southwest to better understand the Colorado River: the dams, the diversions, and the different populations it serves.

My goal was to grasp this mind-boggling system well enough to explain every major development along the river to a fifth grader. This article shares what I learned.

Two excellent books informed my journey—Cadillac Desert (1993) and Where the Water Goes (2017)—with plenty of help from Wikipedia. If I’ve gotten something wrong, or you think I’ve missed an important piece of the puzzle, please reach out: Photographs, unless otherwise noted, are my own.

First things first: an orientation.

While we call it the “Colorado”—and it officially begins in Colorado’s Rocky Mountain National Park—the Colorado River owes its existence to a bivy of tributaries that originate in Wyoming, Utah, Arizona, and to a much smaller extent, New Mexico and Nevada.

credit: Shannon1 / Wikimedia

Those six states—plus California—created the Colorado River Compact in 1922, which determined who can take from the river and who cannot. (In 1944, Mexico also gained some rights.)

The Compact divided the river into Upper and Lower Basins. Arizona sits awkwardly in both basins, but most consider it a Lower Basin member.

credit: USGS

The dividing line between the basins is Lee’s Ferry, just south of the Arizona-Utah border. This is where John Doyle Lee, a Mormon pioneer and leader of the Mountain Meadows Massacre, operated a river-crossing ferry while hiding from federal authorities. Today, Lee’s Ferry is a popular put-in spot for Grand Canyon rafting trips.

According to the Compact, each basin is entitled to divert 7.5 million acre-feet of water each year. An “acre foot” is 326,000 gallons, roughly what 2.5 single-family households use each year.

An acre-foot, explained. (Now multiply by 7.5 million.) credit: Catalina Islander

The predicted flow of the Colorado River—16 million acre-feet a year —was thought to be a conservative estimate in 1922, but the 1910’s were freakishly wet years, so the estimate was actually too generous; recent estimates are closer to 13 million. (From this simple mishap stems far-ranging consequences, which we won’t discuss here.)

The Upper Basin states—Colorado, Wyoming, Utah, and New Mexico—are net contributors to the Colorado: they put in more water than they take out.

The Lower Basin states—California, Arizona, and Nevada—withdraw far more than their tiny tributaries add. And the river’s largest consumer, California, contributes nothing whatsoever. Nor does Mexico.

Before there were any developments on the Colorado, the river flowed all the way to the Gulf of California, creating the Colorado River Delta ecosystem. The river also carries a heavy silt load, and when the silt filled the channels leading to the Delta, the river would carve a new path, flowing northward to (what’s now) Palm Springs. This is how the Salton Sea first came to exist, and before that, a much larger body called Lake Cahuilla. (Lake Cahuilla was also known as Blake’s Sea. Coincidence? I think not.)

Historical pathways of the Colorado River. Credit: NephiCode

Today, the river does not reach the Gulf of California; most is diverted to serve U.S. farms near the Mexican border, and then Mexico diverts the rest for its own farms. This means that the Delta and the Salton Sea receive little or no water, a fact with major environmental consequences. (Environmentalists did score a victory in 2014, when a special “pulse flow” returned water to the Delta for the first time in 16 years.)

Okay, orientation complete. Now let’s answer the question: Where does all this water go? Who uses it? And how does it get there?

The Upper Colorado

The very first users of the Colorado, amazingly enough, are right at the river’s headwaters. They’re actually east of its headwaters, in Colorado’s Front Range.

Before the river even has a chance to pick up steam, the Colorado-Big Thompson Project captures runoff and sends it under the Continental Divide and Rocky Mountain National Park via a 13-mile tunnel to Boulder and Fort Collins.

credit: Northern Water

A little farther down, the Dillon Reservoir—which you’ve driven past if you’ve ever taken Interstate 70 west from Denver—blocks a tributary of the Colorado (the Blue River) and tunnels it 23 miles under the Continental Divide, providing the #1 source of drinking water for Denver as well as irrigation water for Front Range farms.

The tunnel that brings Denver its primary source of drinking water, straight from the headwaters of the Colorado. Credit: 9News

I find it wild and totally fascinating that we’ve drilled multi-mile tunnels under entire mountain ranges to bring water to growing cities like Denver. But hold onto your pants—it gets wilder.

(Also, a disclaimer: I’m only highlighting the biggest and most interesting developments along the river, and I’m sticking to the Colorado River proper. There are many other fascinating developments along the Colorado’s tributaries, such as The Flaming Gorge Dam on the Green River in Wyoming—which Front Range cities may some day attempt to pipe 500 miles over the Rockies to quench their thirst—or the Central Utah Project, which shuttles Colorado River tributary water all the way to Salt Lake City 🤯… so much water to discuss, so little time!)

The next major stop along the river is Grand Junction, where the Colorado (formerly named the “Grand”) meets the Gunnison River, which brings water from far-away corners of Colorado like the ski town of Crested Butte.

Crested Butte snow = future Colorado River water

Grand Junction is the biggest city along the river in the Upper Basin, and river water irrigates over 40,000 acres of local farms— even some high-elevation vineyards. (You may have drunk wine grown with Colorado River water!)

The Colorado River in Grand Junction: picking up steam

Crossing the Utah border, the river skirts Arches National Park and cuts through a gorgeous gorge called “The Portal” before passing through Moab.

“The Portal“ road, east of Moab: a highly recommended drive

Now the river becomes shy and inaccessible as it traverses Canyonlands National Park, where it’s joined by the Green River: its largest tributary and a major silt contributor.

The confluence of the Colorado and the Green in Canyonlands. Credit: The Water Desk

This is the wildest section of the Colorado, including the raging rapids of Cataract Canyon: the same rapids that turned John Wesley Powell’s 1869 expedition into the stuff of legends. For 300 miles, there’s only one place to cross the river by car: the bridge at Hite.

It is here, however, that the wild Colorado—largely unmolested in its journey thus far—becomes tamed.

Glen Canyon Dam & Lake Powell

If you took a plane and traced the path of the Colorado starting at its headwaters, it would remain a small, modest river for much of its journey…

And then you’d see Lake Powell.

credit: Wikimedia

Lake Powell is not a natural formation. It’s created by Glen Canyon Dam, the second-largest dam on the Colorado.


Why do Glen Canyon Dam and Lake Powell exist?

Let’s start with another question: Why do any dams exist on the Colorado?

The basic answers are flood control, usable water, and clean electricity.

The Colorado passes through a desperately arid region: the American Southwest. The soil here doesn’t drain well; the water just tends to run downhill as quickly as it can, which is why “flash floods” happen. It doesn’t rain much here, but when it does, the water collects in monstrous proportions, turning otherwise quiet rivers into raging beasts.

But most of the Colorado’s water doesn’t actually come from rain, roughly 85% comes from snowmelt. Before any human developments were added to the river, the spring runoffs from the mountains of Colorado and Wyoming would swell the river to tremendous proportions, overflowing its banks in the flats and forming unthinkably large rapids in the canyons. Later, in the autumn, the river would become much smaller.

Why is this a problem?

From nature’s perspective, it’s not a problem. From a human perspective, it’s huge problem.

If you live along the Colorado River—in Grand Junction, for example—flooding can be a real pain in the butt. If you were one of the early farmers who used Colorado River water to irrigate your crops, a big flood could wash away your topsoil and spell doom for your crop.

The modern Salton Sea was created, in fact, by heavy flooding of the Colorado around the turn of the century, when an agricultural diversion ditch was overtaken by floodwaters and redirected the entire river into the dry Salton Sink… for two whole years. The Sink became a Sea once again.

Given the choice between feast-and-famine flows—the default state of the virgin Colorado River—or the tame, predictable flows offered by a dam, what would the average anxious farmer or riverside resident choose? They’d choose the predictable flow. And that’s what they’ve chosen, all over the West.

Once you’ve built a dam, you now have a reservoir, too: water that can be saved for drought years, transported elsewhere for consumption by farms and cities, or enjoyed for recreational purposes, as I witnessed on my visit to Bullfrog, a boater’s paradise on upper Lake Powell.

Bullfrog: a marina in the middle of nowhere
Making coffee and reading Cadillac Desert at the Bullfrog picnic area

Finally, dams provide reliable, carbon-free hydroelectric power.

(There are plenty of problems with dams, too, such as fish habitat disruption, silt buildup, reservoir evaporation, and the submersion of communities and natural areas above the dam—I’m just offering a quick overview of why they exist in the first place.)

Now, back to our question: Why do Glen Canyon Dam and Lake Powell exist?

While Glen Canyon Dam does generate hydroelectricity and assist with flood control—and Lake Powell offers recreation opportunities—they weren’t primarily created for any of those reasons. The answer is this:

Lake Powell is a giant savings account for the Upper Basin.

Yours truly, enjoying a paddle on the giant savings account

Let’s go back to the Colorado River Compact and its cardinal agreement: while the Upper Basin (Colorado, Wyoming, Utah, New Mexico) can use up to 7.5 million acre-feet each year, it absolutely must deliver 7.5 million acre-feet each year to the Lower Basin (California, Arizona, Nevada).

Delivering 7.5 million acre-feet downstream is easy to do in wet years, but what about dry years? Consider that the Colorado’s flow can vary dramatically—from 4 million to 22 million acre-feet in a given year (as measured at Lee’s Ferry).

Average annual flows of the Colorado River. Credit: USGS

Imagine you’re an Upper Basin farmer who depends on irrigation water, and the Colorado is only flowing at 11 million acre-feet.

The noisy, populous, and politically powerful Lower Basin will always demand every drop of their legally entitled 7.5 million acre feet… leaving only 2.5 million acre-feet to the Upper Basin. This puts you in the painful position of competing with the other farmers, municipal water users, and industrial users in the Upper Basin.

What do you do? Let your farm go dry? Pay too much money for water? Give up and become a Grand Junction Uber driver?

“If only we (the Upper Basin) had saved the water we had in those earlier, wetter years,” you sigh to yourself, “we wouldn’t be in this predicament…”

…which is exactly why Glen Canyon Dam and Lake Powell were created.

Sitting conveniently above Lee’s Ferry—the dividing point between the Upper and Lower Basins—Glen Canyon Dam allows the Upper Basin to capture surplus flow in wet years and store it in Lake Powell for use in dry years.

Lake Powell can hold 27 million acre-feet. This means that, as long as the lake is reasonably full, the Upper Basin can still use 7.5 million acre-feet in bad years while delivering a full 7.5 million acre-feet to the Lower Basin. All they have to do is release some of the stored water from their giant piggy bank.

Of course, Lake Powell is at the very bottom of the Upper Basin, so to make full use of its water entitlements in a drought year, the Upper Basin also needed to create storage capacity higher up the food chain. That’s why Glen Canyon was just one part of a grander scheme, the Colorado River Storage Project, which authorized the construction of multiple dams and other “projects” (codename for dams and aqueducts) across Utah, Wyoming, Colorado, and New Mexico in the 1960s.

credit: Shannon1 / Wikimedia

These developments give Upper Basin users a sense of security in drought years… and prevented them from starting a water war with Los Angeles, Phoenix, Las Vegas, the Imperial Valley, and other Lower Basin users.

If you’re feeling a bit overwhelmed at this point, this lovely infographic from High Country News might help: it represents the entire Colorado River as a system of buckets (dammed reservoirs) and funnels (river tributaries).

credit: Lester Doré & Holly McClelland / High Country News

Simple, right? 😅

Before we continue our journey downriver, let’s take a moment to acknowledge the Grand Canyon, which isn’t a “development” but important nonetheless.

Carved by the Colorado River over millions of years, the Grand Canyon begins just below Glen Canyon Dam, and the National Park has (thankfully) remained entirely unmolested by dams and reservoirs… but the water flowing into it has not.

Because Glen Canyon Dam traps silt, regulates flows, and alters the water temperature, the water in the Grand Canyon is significantly altered, which means even the “undeveloped” Grand Canyon is far from its natural state. This Wikipedia page explains more.

Hoover Dam and Lake Mead

After passing through the Grand Canyon, the river slows once again, thanks to Hoover Dam: the biggest and baddest development on the entire Colorado.

Hoover Dam with its four intake towers. The verbously named “Mike O’Callaghan–Pat Tillman Memorial Bridge” sits in the background.

Built in the midst of the Great Depression, Hoover Dam created Lake Mead, the largest reservoir in the United States (29 million acre-feet) and a major recreation area for boaters. The dam straddles the Arizona/Nevada border; following a quick security check, you’re allowed to drive over it.

Lake Mead as seen from the Hoover Dam. Note the “bathtub ring” indicating how far below capacity the water line sits.

The 1997 Cadillac Desert documentary, available free online, wonderfully documents the story of how and why the dam was built.

Hoover Dam spurred the creation of modern Las Vegas, which receives 90% of its water from Mead. Recently, the Southern Nevada Water District even funded the creation of a third pipeline to the lake—the “third straw”—which, like the drain of a bathtub, can draw water even if the lake falls precipitously low. This would only happen in a time of utter water crisis, when downstream water users would receive zero water from the reservoir. Clearly, Las Vegas isn’t gambling with its water supply.

Hoover Dam and Lake Mead are the linchpins of the Lower Basin, serving as both storage basin and control valve.

Beyond Las Vegas, no one else draws water directly from the reservoir, so I don’t have much more to say about it… except to share these pictures of Hoover Dam’s magnificent Art Deco men’s room (brought to my attention by David Owen) and a magical campsite—hot springs included!—that lies just a few miles downstream from the dam.

You’ll never pee in a nicer men’s room
Camping just below Hoover Dam at Arizona Hot Springs: an easy 3-mile hike from Highway 93

Davis Dam and Lake Mojave

The Colorado River now heads due south, beelining for Mexico, but soon transforms in Lake Mojave, a small reservoir created by Davis Dam.

Davis Dam, wherefore dost thou exist?

I’m not entirely sure why Davis Dam and Lake Mojave exist. I asked a Park Ranger at Glen Canyon Dam and a volunteer at Glen Canyon Conservancy; neither had an answer.

The Bureau of Reclamation websites says Davis Dam was created to fulfill the United States’ obligation to deliver 1.5 million acre-feet to Mexico each year. But—I wondered—why can’t Hoover do that job? A genuine mystery!

I ended up getting the phone number for Debbie, an administrative assistant at Davis Dam, who connected me to Doug, a Public Affairs Specialist for the Lower Colorado Basin, who in turn pointed me toward this 1941 Congressional feasibility study, which kind of answered my question. Davis Dam was mostly created to generate more hydroelectric power. Fair enough. But what about the Mexico question? The search continues.

From here on out, the Colorado is a “losing river,” which means that more water is taken out than goes in. The average flow rate of roughly 14,000 cubic feet per second at Davis Dam falls to about 2,000 cubic feet per second at the Mexican border. Where does all that water go?

Parker Dam, Lake Havasu, and Two Giant Aqueducts

Continuing south, the river now straddles the border of Arizona and California, becoming wider and shallower, and feels more domesticated as houses and RVs line the shores. River-irrigated farmlands surround the small city of Needles, CA, where flooding destroyed a local bridge three times before Hoover Dam was erected.

For thirty miles, the river becomes the Havasu National Wildlife Refuge—one of the only undeveloped stretches in the Lower Basin before dumping into Lake Havasu.

Growing up in California, I would hear stories of crazy college students who flocked to Lake Havasu on Spring Break to drink excessively on houseboats.

Now that’s how you celebrate water impoundment. Credit: GQ
Woooh Spring Break! (This is me going crazy at Lake Havasu: eating breakfast at 6:30am in a park.)

Back then, I imagined that Lake Havasu was a natural lake that happened to exist in the middle of a desert. Now I know better, and you should too. Lake Havasu was created by Parker Dam, and it’s a special reservoir for a few reasons.

First of all, unlike the wildly fluctuating surface levels of Powell and Mead, Lake Havasu is obliged to stay at a certain height, 440–450 feet, which keeps the surface at a reliable level for recreational purposes.

(When I visited Lake Powell, in contrast, I passed two “lakeside” campgrounds that were closed because the surface level has dropped so significantly in recent decades. A few boat ramps were out of commission, too, because they didn’t actually touch the water.)

Lake Havasu’s consistent height also allows the London Bridge—a bridge they literally imported from London—to continue to look charming each and every day of the year.

London Bridge: not just for Londoners anymore

But Lake Havasu is truly special because it’s where two truly mind-bending developments begin: the Colorado River Aqueduct and the Central Arizona Project.

My interest in water began when I realized that California’s major cities—including Bakersfield and the San Francisco Bay Area, where I grew up and went to college—were utterly dependent on water imported from hundreds of miles away.

Los Angeles is especially fascinating in this regard. In the beginning of the 20th century, William Mulholland, the L.A. Water Commissioner, began searching for new sources of water for his rapidly growing city: a city that only possessed one, tiny, seasonal river (the Los Angeles River) and a rapidly disappearing groundwater aquifer.

Mulholland set his eyes on the sparsely populated Owens Valley in eastern California—and the fast-flowing Owens River, which drains the snowy peaks of the eastern Sierra Nevada—and embarked upon a secretive mission to buy up its farmland and associated water rights. (This story is best told, again, by the Cadillac Desert documentary.) Los Angeles ended up building a 233-mile-long series of canals, tunnels, and siphons—the Los Angeles Aqueduct—that diverts almost the entire Owens river. It continues to do so to this day.

What remains of the modern-day Owens River after L.A. takes its cut.

But that was just the beginning of Los Angeles’ quest. Later, in the 1960s, it would push hard for the California State Water Project, a monumentally expensive and complex series of dams, canals, and pumps that relocates water from northern California all the way down to L.A. and San Diego.

Between these two eye-popping projects, however, came yet another.

Los Angeles was growing so fast in the early 20th century that shortly after the Owens Valley was diverted, William Mulholland knew that it would not be enough. So he looked eastward and devised an ambitious new project: one that would end up in the 1922 Colorado River Compact.

Parker Dam

Completed just two years after Hoover, Parker Dam is technically the deepest dam in the world—but its reservoir, Lake Havasu, only holds 647,000 acre-feet of water. (Compare that to Lake Mead’s 29 million.).

The point of Lake Havasu isn’t to hold a lot of water, but rather to create a nice little drinking fountain for Southern California and Arizona.

In his final act as Water Commissioner, William Mulholland set about creating the 242-mile Colorado River Aqueduct, which would draw water from Lake Havasu and send it through a barrage of pumps, canals, and tunnels until it reached its final destination: metropolitan Los Angeles.

Mulholland succeeded in building almost every ambitious water project he dreamed up—with one glaring exception—and by 1939, water from the Colorado was flowing across the Mojave Desert to sate Los Angelinos’ thirst.

credit: Wikimedia

While I wasn’t allowed to get close to any pumping plants on my road-trip, I was able to walk right up to one of the open canals on my trip and watch the clear, glittering water of the Colorado flow westward.

Let’s pause for a moment to ask ourselves: CAN YOU BELIEVE THIS THING ACTUALLY EXISTS?

From the point of view of early humanity, the Colorado River Aqueduct must sound like the stuff of dreams…or madness. We’re going to STOP A RIVER and PUMP IT OVER AND THROUGH MOUNTAINS and HUNDREDS OF MILES ACROSS THE DESERT to a city in MIDDLE OF NOWHERE.

The Colorado River Aqueduct intake pumps at Lake Havasu. Credit: KTLA

Yet projects like these are exactly what sustain the 20 million residents of Southern California. This is the world we live in.

Back when it was approved, The Colorado River Aqueduct made Arizona quite upset, because they (correctly) sensed that California planned to suck up as much Colorado River as they could, with no consideration for its next-door neighbor. Arizona even sent 100 National Guard soldiers with machine guns to halt construction of Parker Dam on the Arizona side of the river.

Long story short, Arizona eventually got its way with the 1968 approval of Central Arizona Project: a 336-mile aqueduct from Lake Havasu to Phoenix and Tucson.

The Mark Wilmer Pumping Plant pushes water from Lake Havasu 800 vertical feet to the beginning of its journey to Phoenix and Tucson
credit: Mountain Town News

When I drove to Tucson, it seemed inconceivable that the Colorado River could have traveled so far. Yet there it was, in plain sight.

Colorado River water arriving at the C.A.P. Twin Peaks Pumping Plant outside Tucson


Both the Colorado River Aqueduct and Central Arizona Project require huge amounts of electricity to pump the water over the various mountains that stand between Lake Havasu and their final destinations. Much of this electricity is provided by the dams themselves, but sometimes even that is not enough.

The Central Arizona Project spurred the creation of the Navajo Generating Station, a coal-fired power plant nearby Glen Canyon Dam that became the largest power-generating facility in the West. The plant provided high-paying jobs to the Navajo Nation for many decades… and also spewed pollution. In 2019 the plant was closed and the smokestacks were demolished; I couldn’t see them as I drove past.

Interestingly, the plant wasn’t closed for environmental reasons—it was primarily closed because the price of energy was driven down so precipitously by fracked natural gas that coal energy became economically unviable.

Toppling smokestacks at Navajo Generating Station in 2020. Credit: Power Magazine

Alright, back to the river!

Imperial Dam and the All-American Canal

As the Colorado makes its way down the California/Arizona border, two tiny dams—Headgate Rock and Palo Verde—divert part of the river into irrigation canals for the Parker and Palo Verde Valleys. These are called “diversion dams” because they don’t create reservoirs, they simply divert the water.

Then the Colorado hits the biggest diversion dam of them all: Imperial.

The Imperial Dam complex. The desilting basins on the left lead to the All-American Canal; the remaining Colorado River heads downwards; and the Gila and Yuma projects draw water from the right. Credit: BOR via Maven

At Imperial Dam, a full 90% of the Colorado River is diverted for agriculture in the southernmost parts of the United States: the farmlands of Yuma, Arizona, and Imperial Valley of California.

The Imperial Valley is the big player here, and it was one of the main reasons that Hoover Dam was created in the first place.

Growing up in California, I didn’t really know that the Imperial Valley existed. Sure, it was there on the map, but it didn’t have any big cities. It just looked like boring farmland.

credit: Bloomberg

Little did I know that that this boring farmland produces the vast majority of America’s winter vegetables, most notably lettuces.

The valley itself is a parched desert, but its soil and sunshine is insanely well-suited to agriculture; all it needs is water. Around the year 1900, farmers were already diverting water from the Colorado via the Alamo Canal, but the river was a wild beast. (Remember, that’s how the Salton Sea was mistakenly created.) Also, the Alamo technically traveled through Mexico for a while, which worried the United States. So when federal authorities authorized the construction of Hoover Dam, they also authorized a diversion dam—Imperial Dam—and a new canal that would only travel through America: the All-American Canal.

It’s surprisingly easy to trespass along the All-American Canal

The All-American Canal is a BEAST. It’s the largest irrigation canal in the entire world, and it’s the only source of water for the entire Imperial Valley… beyond the 3 inches of average annual rain, which farmers consider a nuisance. (Rain is far less predictable than Colorado River water.)

The All-American Canal just below Imperial Dam
The All-American Canal, as seen off Interstate 9, just before the Coachella Canal diversion

The canal travels 82 miles—much of it skirting the U.S./Mexican border—and even cuts straight through a massive sand dune.

The AAC in the Algodones Dunes. Credit: Charles O’Rear via Wikimedia

Following the canal into the Imperial Valley, I even discovered (who seem to be) the very first water users: some happy cows in a green pasture.

Colorado River water flowing through “East Highlight Lateral Eight” near Holtville Hot Springs; happy cows in the background. (An irate farmer yelled at me from his truck shortly after I took this photo.)

A recent addition to the All-American Canal is the Warren H. Brock Reservoir, a square puddle alongside Interstate 8 that captures “underutilized” water before it reaches the Imperial Valley. Really, this is a way of ensuring that America doesn’t send a single drop of extra water to Mexico.

That curious square of water in the middle of the desert? The Warren H. Brock Reservoir. Driving along Interstate 8, you might never notice it.

It takes five days for water to travel from Lake Mead to the Imperial Valley. If the Imperial Irrigation District places a water order and then, two days later, a sudden storm rolls into the Valley, the farmers might harm their crops through overwatering. They need to reduce their order, but the water is already on its way. In the past that extra water would be allowed to flow to Mexico via Imperial Dam; now, it heads down the All-American Canal and ends up in Warren H. Brock, where it can be released again later. Tricky tricky, America!

The All-American Canal also waters the Coachella Valley (i.e., the Palm Springs area) via a 122-mile spur, the Coachella Canal. I snapped a picture of this canal just above Slab City, the squatter community popularized by the movie Into the Wild (here’s the scene).

Coachella Canal above Slab City. This (huge) canal is just a fraction of the All-American Canal.

Another unique feature of Imperial Dam is the desilting basins, which slow the water down and let the silt sink to the bottom, where rotating scrapers remove it and redeposit it downstream. That’s why All-American Canal water looks perfectly clear and clean, instead of brown and silty as Colorado River water normally would. This blog post documents the desilting basins and other impressive features of Imperial Dam.

If you’re wondering where most of the Colorado River goes, you now have the answers: Southern California, Arizona, and the Imperial Valley. But the story isn’t over yet.

A salt-free water vending stand outside Yuma, Arizona.

Yuma and Mexico

One of the final places to receive Colorado River water is the city of Yuma, Arizona. When I rented an Airbnb room there, I went for a run on a path paralleling a nearby canal. When I came back, I asked my host, a retired schoolteacher, whether the canal contained Colorado River water. She’d lived there 20 years; she didn’t know where the water came from.

It did indeed come from the Colorado.

The East Main Canal in Yuma: a lovely place for a run

Following that canal took me to downtown Yuma, where I spotted another canal: one that that was lower, smaller, and stinkier.

This was a canal I’d actually been searching for. With some judicious Google Map sleuthing, I knew I’d found it: the Main Outlet Drain.

When the United States promised in 1944 to deliver 1.5 million acre-feet of Colorado River water to Mexico each year, nothing was said about the quality of the water, which was palatable until 1961, when the Bureau of Reclamation completed a canal-lining project that returned salty agricultural runoff from Wellton-Mohawk farms (east of Yuma) back to the river. Wellton-Mohawk has a particularly bad salt problem, and the runoff made the water that passed in Mexico totally unusable for farmers in the Mexicali Valley.

What happened next is best described by Marc Reisner in Cadillac Desert:

[Mexican] President Luis Echeverría campaigned heavily on the [Colorado River water quality] issue, and, after winning the election, threatened to keep his promise to haul the United States before the World Court at The Hague. In 1973, for reasons which are still obscure—but which might conceivably have something to do with the fact that Mexico showed some promise of owning a great deal of oil—President Richard Nixon appointed a former U.S. Attorney General . . . to work out a hasty solution.

In Where the Water Goes, David Owen adds:

One reason [for the American government’s change of heart] was concern among American officials that, if the United States took a hard line on the river, an ominously left-leaning Mexican government might be tempted to ally itself with the Soviet Union. Another reason was that irrigators in the United States had salinity issues of their own, and they came to believe that, if the American government would do something to address Mexico’s problem, American farmers might come out ahead, too.

Geopolitics at its best!

One of America’s solutions to the salinity problem was a multi-hundred-million-dollar desalination planet in Yuma—a plant that was only ever briefly operated twice, yet still remains today, doing a whole bunch of nothing.

The Yuma Desalination Plant: only $500/acre-foot for less salty water. credit: BOR

Another, more graceful solution was found in 1977: the creation of a drainage canal that moves 100,000 annual acre-feet of salty runoff directly from Wellton-Mohawk farms into Mexico, dumping it in the Colorado Delta. With this simple fix, the Colorado River water entering Mexico dropped below the agreed-upon threshold of a thousand parts per million.

This might sound like the story of a rich country dumping its problem onto a poor country. But the canal—the Main Outlet Drain—was also single-handedly responsible for creating what is now a valuable ecological area: the Cienega de Santa Clara.

Pajaros ❤️ La Cienega de Santa Clara. credit: El Sol de México
credit: Grace Cook

The Cienega is so beloved, in fact, that if the Yuma Desalination Plant ever actually operates, environmentalists worry that the super-saline reduced runoff would harm the wildlife that now thrives there.

This story parallels that of the Salton Sea: if Imperial Valley farms improve their conservation practices, less runoff will reach the Sea, reducing its capacity as a migratory pitstop for birds.

These are the fascinating contradictions of the contested Colorado River.

An irrigation canal parallels the Mexican border near Gadsden, AZ.

At the very end of the line, just across the Mexican border, is Morelos Dam.

This is effectively where the Colorado River ends; Morelos diverts the salty, silty water to farms in the Mexicali Valley and a few nearby cities.

Morelos Dam. The aqueduct goes left; what remains of the Colorado goes right. credit: Yale

Pull up Morelos Dam on satellite-view Google Maps, and trace the path of the Colorado southward, along the U.S./Mexican border. Nothing more than a dry riverbed remains.

The modern-day Delta. Credit: Sierra Club

That’s the very short story of the Colorado River: where it goes, who uses it, what’s built on it, and why.

To learn more about this complicated and fascinating river, I recommend starting with Where the Water Goes by David Owen.




Blake Boles

Author: Why Are You Still Sending Your Kids to School? / Founder: Unschool Adventures /