In the Colorado River basin, our past has come back to haunt us.

We’re not just talking about the dead bodies emerging from the drying shoreline of Lake Mead. The river’s water crisis has caused the nation’s two biggest reservoirs to sink to historic lows.

It’s a problem of our own making — in more ways than one.

The Colorado River Compact, signed a century ago, overallocated the river’s water. Experts have long warned that nature can’t continue to deliver the water that the government has promised to farms, cities and towns.

A drying West, warmed by climate change, has now made that shortage impossible to ignore.

For years demand has outstripped natural flows on the river, and some states and Tribes have already taken cuts to their allocations. Additional conservation measures were expected as the seven U.S. states that share the river — Colorado, New Mexico, Utah, Wyoming, Arizona, California and Nevada — have been working on hammering out a new deal. The region’s more than two dozen federally recognized Tribes have also been fighting for a seat at that table and a hand in the river’s management. But the deadline for a revised agreement between all the parties came and went this summer with no resolution in sight.

To say there’s a lot at stake would be an understatement.

Some 40 million people rely on the 1,400-mile-long river in the United States and Mexico, including in many of the West’s biggest cities. It also greens 5 million acres of irrigated agriculture.

But that’s come at a cost. Long before cities and industrial farms emerged, the river supported diverse mountain and desert ecosystems, providing refuge and resources for countless animals and plants.

Many of those species now struggle to survive the cumulative pressures from drought, climate warming and human developments. And they remain an overlooked part of the region’s water crisis.

“The story continues to be about water supply and water management, and how to continue to drain the river to support the growth economy,” says Gary Wockner, executive director of the nonprofit Save the Colorado. “There’s been very little discussion about the ecological health, wildlife and habitat.”

Hot drought

A lot can happen in two decades.

In 2000 Lake Mead and Lake Powell, which help manage water supplies along the Colorado, were nearly full. Today they’re both hovering just above one-quarter capacity — the lowest ever since being filled.

In the intervening 20 years the Colorado River basin has seen a prolonged drought that’s now believed to be the driest period in the region in the last 1,200 years. River flows have fallen 20% compared to the last century’s average.

And it’s not just from a lack of precipitation. Researchers attributed one-third of that reduced river flow to climate change. Warming temperatures increase evaporation, as well as evapotranspiration by plants. So even when the Rocky Mountains do receive snow or rain, less of that runoff makes it to the Colorado River and its tributaries.

Experts say we’ll see more of these so-called “hot droughts” as the climate continues to warm. The basin is expected to see a five degree-Fahrenheit jump by 2050. That will make things not just hotter but drier. If we don’t dramatically cut greenhouse gas emissions, the Colorado’s flow could drop 35% to 55% by the end of the century.

Years ago the region’s prolonged drought was dubbed a “megadrought,” but some of the region’s top scientists say “aridity” may be a better term. That means that the combination of warming and drying will be much more permanent.

Aridity and animals

The region’s ecosystems — and those who live in them — are feeling the heat.

“Climate warming is just hammering this basin, and part of what we see in addition to the water disappearing is this protracted wildfire season,” says Jennifer Pitt, the Colorado River program director for Audubon, the bird-conservation organization. “The fires are more intense and cover ever-larger landscapes, that in turn has the possibility to severely impact the health of the watershed.”

Millions of trees have also been lost to insects and disease exacerbated by drought, including along riverbanks, where less shade is warming streams. Many desert plants, like ocotillos, Washington fan palms and Joshua trees, are also declining from warming temperatures, less precipitation and thirstier animals.

Across the region streams and springs are drying up, too, leading to declines in populations of aquatic amphibians, fish and insects that make up the base of the food chain.

“We haven’t seen any entire species go extinct yet,” says Michael Bogan, an assistant professor in the School of Natural Resources and the Environment at the University of Arizona. “But if you project this into the future, that’s certainly something we’re worried about.”

His concern includes the fate of endangered desert pupfish and Gila topminnows.

“They used to be present in large river systems, but the changes in the habitat and the introduction of non-native fishes have basically excluded them from all of those large historic habitats,” he says. “Now the only refuge where they can survive is these smaller habitats — these headwater streams and springs — and those are the exact types of places that are disappearing now.”

Birds are at risk, too, a recent study found. The researchers visited areas of the Mojave Desert that had been studied in the previous century and found that, on average, the sites lost 43% of their species. The main driver, they believe, is decreased precipitation from climate change.

Birds who live in the desert already endure harsh conditions, but climate change could push them past tolerable limits, causing lethal hyperthermia or dehydration. A lack of water can also cause reduced fitness and or force birds to skip a breeding cycle.

We already see this happening with burrowing owls. A study by researchers from the University of New Mexico looked at how increasing air temperature and aridity affected the species.

Between 1998 and 2013 the birds at their study area in New Mexico experienced a decline in the number of young that left the nest and a precipitous 98.1% drop — from 52 breeding pairs to just one.

The researchers associated the declines with the effects of decreased precipitation and increased temperature. “An increasingly warm and dry climate may contribute to this species’ decline and may already be a driving force of their apparent decline in the desert Southwest,” they concluded.

Mammals aren’t immune to the changes, either. Another recent study found grave threats to pronghorn across the region. Their models predicted that half of the 18 populations they studied would disappear by 2090.

A decrease in water supply affects animals’ health but can also cause behavioral changes that could put them in harm’s way. If animals need to move outside their normal range in search of declining food or water, it could lead to more interactions with predators or more human-wildlife conflicts, especially if animals look for resources in more urbanized areas.

Fewer sources of water also force a greater number of animals to congregate at the remaining watering holes. Experts say this increases the risk of disease outbreaks like the one that happened in 2020 along the Pacific flyway in California and Oregon, when 60,000 birds crowded into sparse wetlands perished from avian botulism.

An altered river

Many of the most severe ecosystem impacts currently affecting the Colorado basin predate the 20-year drought.

Hoover Dam’s construction in 1936, followed by the building of Glen Canyon Dam 30 years later, dramatically altered river’s flow, blocked sediment that creates riparian habitat, and changed the temperature of the river.

“The Grand Canyon is a completely different hydrologic and ecological cycle than it was before [Glen Canyon] dam was built,” says Wockner.

Today the 360 miles between the two dams, which include the Grand Canyon, have become “a river that’s managed to pool-to-pool,” says Pitt. “There’s not much flowing river once you get below Hoover Dam.” That’s caused a loss of riparian forest, which supported birds and other wildlife, and pushed four native fish — humpback chub, bonytail chub, Colorado pikeminnow and razorback sucker — to the brink of extinction.

“There’s concern for quite a number of species because of the historically altered river flow,” says Pitt.

It also decimated 1.5 million acres of wetlands downstream at the Colorado River Delta in Mexico.

“For most of the last 50 years, the river has not flowed to the sea,” says Pitt. “An untold wealth of wildlife disappeared off the map because of the desiccation of that landscape.”

Compounding problems

Development, dams and water diversions along the Colorado, along with today’s drought and climate warming, have pushed many species to the razor’s edge. Some are barely hanging on.

Of particular concern right now are humpback chub, which suffered after Glen Canyon Dam’s construction. Managers have spent decades trying to recover the fish — with some recent success.

But now the species faces a new threat: non-native largemouth bass — a voracious predator of humpback chub — who thrive in the warmer water that’s being released from the diminished reservoir.

In June researchers detected the fish downstream of Glen Canyon Dam, in the same habitat where humpback chub numbers were finally improving.

“The National Park Service is really worried that if those populations of non-native fish get established in the Colorado River downstream from Glen Canyon Dam, that could be catastrophic for the humpback chub,” says Pitt.

The situation is emblematic of the larger ecological consequences stemming from our river management.

“How we manage the dams and the water levels is directly affecting the ecology of the Colorado River itself,” says Bogan.

And while that imperiled ecology may not be the headline news regarding the Colorado River crisis, its significance shouldn’t be understated.

Millions of people visit the Grand Canyon each year to peer over the canyon’s lip and glimpse the Colorado’s path through the ancient towering walls. They come, too, to see California condors, bald eagles and southwestern willow flycatchers — all of whom could disappear if the river does.

The loss of plants and animals across the basin is also a loss of cultural resources for the region’s Tribes.

And as the river declines, so does everything around it.

“The hydrological cycle is the cycle of life on the Earth,” says Wockner. “That’s true everywhere, but it’s especially easy to see in a desert environment like the southwestern United States where so much diversity and abundance happens in streams, at the edges of streams, near streams. As you drain the river, you drain the life off the land that depended on that water.”

Worse before it gets better

As states work to deal with shortages of water from the Colorado River, there’s a chance that things could get worse before they get better.

One concern is an overdrafting of groundwater, particularly in Arizona, which legally bears the brunt of shortages on the Colorado and has many areas where groundwater pumping is not regulated.

That can leave groundwater-dependent springs and streams at risk of drying.

Another area of concern is California’s Salton Sea — the famously saline lake in the desert fed now only through agricultural runoff from the neighboring irrigation districts. One of those is the Imperial Irrigation District, which gets the biggest chunk of California’s Colorado River allotment. As the region attempts to work out a new plan to decrease water use, there’s pressure on the agency to fallow some of its 475,000 acres, but that would also mean less runoff making it to the Salton Sea.

“The Salton Sea is some of the only remaining habitat for migrating water birds and shorebirds in interior California,” says Pitt. “The Central Valley was that habitat once upon a time, but has been completely developed. So it’s a critical habitat for many species.”

It’s also a public health threat. As winds sweep across the drying lake, particles of dust and pollution are swept into neighboring communities where residents suffer from high rates of asthma and respiratory problems.

“The answer is not that we can’t reduce any water use from the Imperial Irrigation District,” she says. “As uses of water are reduced in irrigated agriculture that drains to the sea, there needs to be mitigation.”

A plan, that includes habitat restoration and dust mitigation suppression projects, created decades ago to do just that has been slow to get off the ground. It needs to “ramp up quickly to protect wildlife and to protect public health,” she says.

The path forward

There is some good news.

Agreements between Mexico and the United States in the past decade have enabled “pulse flows” of water to flow downstream to repair a small amount of the lost wetland habitat in Mexico’s California River Delta. And in the desert, fortunately, a little can go a long way.

“We’re seeing improvements in both the number of bird species detected there and the populations of those species,” says Pitt. She’s optimistic that the two governments will continue to support that environmental program in the future.

It’s an idea that could help upstream habitat as well.

“I think really the most important thing that’s being done at both the state level and at the local level is trying to get dedicated flows in streams that are explicitly for the conservation of aquatic species,” says Bogan. Although right now, because of the complexities of water rights, that work is limited and usually local in scope.

“But it’s something that at least has given me a little bit of hope,” he says.

Another strategy, says Pitt, is “natural distributed storage,” which means restoring wetlands and high-elevation meadows to slow water down as it runs across the landscape. That can help recharge groundwater and provide moisture to soil and plants.

“The more moisture we’re keeping around the less vulnerable these areas are to fire,” she says. “It will have an incredible wildlife benefit because those meadows are rich habitat.”

It’s akin to the work that beavers do naturally, but people can replicate.

“It sounds small if you look at it on one little creek,” she says, “but if we can start to see it implemented across the upper basin, I think it could really scale up to make a difference.”

With the cumulative impacts of human development and climate change adding up, Pitt says we should look to the federal government and states to make sure that Endangered Species Act programs are supported to help protect and restore habitat for the dozens of already at-risk species in the basin. This means going beyond supplementing the number of endangered wild fish with hatchery-raised fish, which is the current management strategy.

And of course, the region still needs to grapple with how it allocates and manages the Colorado River’s water. Pitts says she’d like to see a greater role for Tribes in that process and the inclusion of adequate water to maintain healthy ecosystems.

“Environmental water needs to be recognized as part of our objectives for water management,” says Pitt.

“It’s both extremely challenging at this moment because there’s so much less water available to carve up between users,” she says. “But it’s a moment to really rethink how we do things.”

That rethinking should include changing how the river’s water is valued, says Wockner. If economy continues to trump ecology, the river basin will continue to decline.

“I don’t see environmental protection or ecological health rising to the forefront in any of the discussions,” he says. “I think as the chaos and crisis escalates, the environment is going to continue to be the biggest loser without a voice at the table. Because it’s all about trying to save the economies in the southwest United States that are dependent on the draining of the river.”