The Colorado River doesn’t flow like it used to.
Massive concrete dams tame its historical flood patterns. Thirsty farms and cities siphon away more and more water. And climate change is supercharging evaporation and drought.
That’s bad news for everybody, but especially the green giants that tower over scrubby desert riverbanks. Cottonwood trees have become increasingly elusive.
“There's one cottonwood tree here. There's maybe another one over there,” Matt McEttrick said as he pointed across the Colorado River in southeast Utah. “But we should be seeing tens — hundreds, probably — at this site, rather than just two.”
A century ago, this riverbank on the southern edge of Arches National Park would have looked very different, said the southeast area manager for the Utah Division of Forestry, Fire and State Lands. The spot where McEttrick stood would likely have been the middle of a shady cottonwood forest that covered the canyon floor from one red rock wall to the other.
Today, however, the pale dirt under his and Liz Ballenger’s feet cracked and curled in the hot sun. It’s not a great sign for the future of a tree at the heart of many desert river ecosystems.
“We're not going to see — probably — extinction of cottonwood, by any means,” said Ballenger, a biologist for southeast Utah’s national parks. “But seeing its decline in the river corridor is troubling.”
What’s starkly absent on many riverbanks are younger generations of cottonwoods. That’s because saplings depend on the periodic floods that historically pushed water up onto riverside terraces.
That’s not something we see anymore, Ballenger said. Because so many dams and diversions upstream keep water levels low and controlled, “we're not getting the scale of floods that used to happen in this area.”
Decades ago, McEttrick said it was common for the Colorado River to reach 50,000 or even 100,000 cubic feet per second during floods. These days, however, a typical flow rate for the river may be just 3,000 or 4,000 cubic feet per second.
That means baby trees far from the main channel are left high and dry. And the ones that sprout right next to the river often get swept away.
“The cottonwoods are still here,” McEttrick said. “Every year, you still see thousands of seedlings. They're just not surviving.”
It’s a common sight in riparian areas across the West, and the ripple effects are significant.
In a region without many tall trees, a cottonwood offers vital habitat for eagles, herons and other birds, such as the threatened yellow-billed cuckoo. Its bark, stems and foliage provide food for beavers, deer and rabbits.
When its leaves fall into the river each autumn, they boost the aquatic food cycle, adding nutrients to the water and helping native fish. The leaf litter also tweaks the chemistry of the surrounding soil and water as it decomposes, sustaining fungi and maintaining a delicate balance of nitrogen, carbon and other elements.
“It's potentially a keystone species out here in the plant world,” Ballenger said. “There's just something so iconic and magical about this large tree that grows in our riparian systems, and our riparian systems are the lifeblood of the desert.”
In the cottonwood’s absence, invasive trees like tamarisk and Russian olive have often filled the void — but without serving the same ecological functions.
None of the solutions to this problem will be easy, McEttrick said. Reversing the changes that led to cottonwood’s decline will likely require difficult choices about water use and management.
“There's just been some important Jenga blocks that have been pulled out,” he said. “We can help hold that thing up for now, but eventually we're going to have to have some blocks to put in there.”
There are actions people can take in the short term to buy cottonwood trees some time. One is protecting mature cottonwoods by removing invasive plants and preventing wildfire damage.
Arches National Park has also planted some young trees near campgrounds and visitor use areas, Ballenger said. Getting them established has proved to be a challenge, however. During an average water year, she said, fewer than half of the seedlings planted without irrigation typically survive.
Some researchers are even looking at transplanting alternative cottonwood varieties from hotter, drier parts of the Southwest in hopes they can better handle Utah’s new climate reality — a process known as assisted migration.
Another key piece is ensuring individual waterways are as hospitable as possible for new trees.
For the past five years, Kristen Redd has been working to restore a section of Indian Creek at The Nature Conservancy’s Canyonlands Research Center, where she’s the program manager. The creek is a tributary that flows into the Colorado River in nearby Canyonlands National Park — well, sometimes, at least.
“This creek used to be perennial, which means that it almost always had water in it,” Redd said, as she stepped across a bed of dry cobblestones. “But with climate change, we're seeing less and less perennial water in this creek.”
That makes it all the more important to make the most of the water it receives.
So, Redd’s team has turned to low-tech process-based restoration. The work involves some routine tasks, such as pulling weeds and planting native grass seed. The centerpiece, however, is digging trenches in the riverbed and filling them with wooden posts and rocks. It’s meant to mimic the beaver dams that were once common across the region.
“What we're trying to do is just hold the water back on the landscape,” Redd said. “So, instead of the water rushing through the system and heading for the Colorado River, heading for Lake Powell, we're looking to create areas of pooling water.”
That’s just what a growing cottonwood needs.
Redd leaned over a mound of sediment that’s built up behind one of the structures she helped install a couple of years ago and pointed toward a promising sign: a patch of tree seedlings that have sprung up on an embankment.
Using drones and lasers, Redd’s team mapped the riparian areas that surround Indian Creek to measure the project’s progress. During some flood events, the creek has gone from 2 feet wide to 20 feet wide in places, she said.
The hope is that nature will begin to heal on its own after the restoration work takes it partway there.
“The willows and baby cottonwoods coming in — it's just incredible,” Redd said. “The desert just responds to water.”
There are additional benefits to slowing down water and distributing it over a wider plain, too. It can prevent some of the destruction that floods often cause and also help recharge groundwater aquifers.
The Trump administration’s decision to hold back federal funding could slow the project’s progress, however. In early 2025, Redd’s team was approved for $1.5 million in Bureau of Reclamation Colorado River Environmental Funding to continue restoration efforts on Indian Creek. She said that money has since been frozen.
What scientists and conservationists have learned at the creek so far could still help cottonwoods in other riparian areas across the Colorado River Basin, though.
“If we can start to scale that work up — not just one stream here and one stream there but really scale it up at the watershed scale — then I think we can really start to see an impact,” said Alix Pfennigwerth, who manages riparian restoration projects with The Nature Conservancy.
This summer, her team will launch its first efforts to do just that.
Pfennigwerth will work with the Bureau of Land Management to rehabilitate roughly 2 miles of another stream in southeast Utah, in addition to similar projects in Colorado and Wyoming. It’s part of a 5-year, $10 million collaboration to increase the number of stream miles being restored and to simplify policy and permitting regulations so there are fewer barriers to doing this type of work in the future.
While the term “low-tech process-based restoration” may be novel, the techniques are not. Indigenous peoples of the Southwest, including the Zuni, have long used earthen dams to slow down and spread out water. That’s on top of all the ways beavers have shaped riparian areas for millennia.
So, these projects represent one small step toward using the Colorado River’s past to protect its future.
“This is not a new thing. This was not discovered or invented recently,” Pfennigwerth said. “We're just trying to bring some of those processes back to streams where it's been lost.”
This story was produced as part of the Colorado River Collaborative. KSL TV photographer Mark Wetzel contributed to this story.
