As Lake Powell Dries Up, Mud Threatens Its Future

“Don’t stand behind me,” says Cari Johnson, as she digs a small gardening hoe into a steep slope above the Colorado River in Utah’s remote Cataract Canyon in an attempt to climb. “This is all loose.”

Her warning is well-founded. As the University of Utah geology professor places one foot on her newly carved step, it gives way underneath her. “This one’s coming down,” she shouts as a basketball-sized clay boulder begins to tumble, sending up plumes of fine dust.

This slope is not made of the hardened sandstone that forms the towering cliffs of the surrounding desert canyon. Johnson is studying an unstable Frankenstein’s monster composite—made up of loose sand, fine silt, cobblestone, mudstone, and clay. Much like traversing on top of an icy glacier, one wrong step on what appears to be stable ground can prove disastrous, collapsing down into steep gullies or hidden crevasses.

The material is so perilous because 10 years ago, in this very spot, we would have been standing at the bottom of Lake Powell, the nation’s second-largest reservoir. For more than half a century after the Glen Canyon Dam was constructed, the massive lake hid parts of Cataract Canyon beneath its still waters, turning it into a giant settling pond for the roughly 18 million tons of sediment the river moves every year. In September the reservoir dropped three feet lower than the previous low point set in 2023; if it drops just 29 feet more, the dam will stop generating hydropower. Many boat ramps at the summer recreation hotspot no longer reach the water’s edge, and a stark white bathtub ring on the canyon walls is larger than ever.

The lake is so parched the Colorado River is now flowing in reaches it hasn’t meandered through since the 1960s. But it’s not charting the exact same path it did back then. Instead of flowing over bedrock, it’s carving through an enormous mud shelf—100 feet deep in some stretches. This area could easily be dubbed Mudtopia. The river flows over mud rapids, which churn up whitewater from hardened clay. Mudbergs, craggy and gnarled, rise up from the channel, easily snagging propellers from inattentive boaters. Mud volcanoes, shaped just like a 10-foot-wide replica of Mauna Loa in Hawaii, burp methane generated from decaying vegetation buried in the layers in big enough volumes you can light them on fire. A massive mud glacier formed in the reservoir’s delta is slowly creeping closer to the dam.

Then there are the slumps, basically mud avalanches, one of which is starting to collapse under Johnson’s feet. Because the sediment shelves rise taller as the river incises its new muddy channel, eventually gravity takes hold and topples sediment back into the water. Some slumps are small. Others are massive. One in 2024 slid into the river, temporarily dammed it, and created dangerous new mud rapids. Another in 2023, billed as the “Space Slump,” was large enough one could easily see the river’s new contours on satellite imagery.

Since around 2017, the area has attracted thrill seekers and scientists to explore this newly revealed world. But as the river reclaims its old channel, the mud it moves carries threats. Sediment intrusion could clog the dam’s hydroelectric infrastructure. Piles of mud on its bottom limit the reservoir’s storage capability. Lake Powell has already lost nearly 7 percent of its total storage due to the piling sediment, or 1.8 million acre-feet of water. That’s about nine times the amount Nevada uses from the river annually. Those storage losses could accelerate even further if the reservoir remains critically low and more of its former lake bottom is mobilized, Johnson says.

As these massive slumps supercharge the Colorado River with even more sediment than it naturally carries, the question is where all that material ultimately ends up. Because of the dam, it’s trapped. “So it’s stacking up,” Johnson says.

That’s why a consortium of longtime river runners and scientists like Johnson have undertaken the quest to track and monitor this dynamic landscape. To them, it’s not enough to worry about the volumes of drinking and irrigation water disappearing. “We are trying to daylight the sediment part of this story,” Johnson says. “It’s easily ignored.” She wants to study this landscape to help bring scientific answers to the often politically-charged debates about Colorado River management. Plus, it’s an irresistible chance to see geologic processes that usually take millennia play out over decades.

To understand it all is a monumental task. “You really need to move over there,” Johnson says as she nears the top of the 30-foot slope. A few moments later, another slab begins to slide.

Today’s scientific effort to study the mudflows can be traced to an unusual origin point: A welding shop in Moab, Utah. Opened in 2012 by longtime river runner Mike DeHoff, Eddyline Welding became a hub for locals to custom build their raft’s oar frames or make repairs to boat trailers. “That welding shop became like a bug light for river runners,” Meg Flynn, DeHoff’s wife and collaborator, says. As adventurers came through, they talked about the dynamic, sometimes frightening, changes happening in Cataract Canyon and compared observations.

Cataract has a reputation among river runners for being rough and intimidating, but the retreating reservoir has revealed its multifaced nature. “It’s like an art museum and a science museum and a playground and a sanctuary,” Flynn says.

Flynn, a librarian in Moab, and DeHoff first compiled a field guide to the changing landscape. Maps of Cataract Canyon had become outdated as slumps reshaped the river channel and rapids roared back to life. The latest to emerge, called Gypsum Canyon, was a small wavelet in 2022. Now it’s churning with whitewater as the river has excavated mud covered boulders. Guidebooks just a few years old fail to mention it.

What began as a curiosity became an obsession. In 2019, they and a few river running friends formalized their efforts under the Returning Rapids Project. The group has set out to document the changes happening in the transition zone between the Colorado River and Lake Powell, combining repeat photography, archival footage, river maps and field observations with scientific research. Project staff regularly take groups of scientists and policy experts out on trips on both the Colorado River and the San Juan, another tributary that empties into Lake Powell. “I’m always amazed at how they read the river,” Johnson says. “They’re pointing out geomorphologic changes I wouldn’t have even noticed.” Every year, the project publishes a report with findings from their trips, and puts it in the hands of decision makers at the National Park Service or other federal agencies tasked with river and reservoir oversight.

DeHoff and the Returning Rapids project are no longer just river guides. They’re trying “to assist in helping with the Gordian knot that is management of the Colorado River,” DeHoff said.

Earlier in the day, the Returning Rapids crew launched two small metal motorboats from a ramp near Hite, Utah, within eyeshot of an abandoned marina left marooned from the reservoir’s retreat.

The boats veered upstream along the Colorado River, deep into the heart of Cataract, sending small wakes into the sediment shelves that line the river. Chunks of mud tumbled into the water as the ripples made an impact.

Taking measurements of this kind of landscape requires patience and a steady boat captain. While riding in the tiny boat, Johnson attached a GoPro camera to the end of an extendable painter’s pole. She extended it dozens of feet into the air, right next to the sediment shelf. The boat zig-zagged parallel to the collapsing ledge, causing the extended pole to wobble while capturing thousands of images. Johnson can then feed the photos into a model that gives her a sense of the shelf’s height and volume. Make enough of these images, and scientists could predict when and how sediment moves deeper into the reservoir and where the new mud will accumulate, Johnson said.

Later, at a newly exposed riffle, Johnson climbed out of the boat and onto a mid-river gravel bar to take a sample. When the river carves away enough mud, it can hit bedrock and suddenly form a waterfall, a dangerous obstacle for any boat. Johnson used her metal hoe to cleave a portion of rock off to try and understand just how quickly it might erode if the river’s flow ramps up.

The research can be applied to aid in reservoir management and keep boaters safe. It’s also just fascinating to see a potential waterfall form in real-time, Johnson said. She made her career studying rock layers from the Earth’s deep time. But most of these sediment deposits have formed in the blink of an eye on the geologic timescale, about 60 years. They wound up here, in the transition zone between the Colorado River and Lake Powell, because of human decision-making and infrastructure-building more than any natural force. Studying how sediments move within reservoirs can yield insights for water management around the world, Johnson said, as water scarcity and climate change puts human infrastructure to the test.

“I think of this whole system as probably the greatest experiment I’ll ever have been a part of,” she said. “‘Greatest’ meaning it’s a cool experiment, not necessarily that it was a wise thing to do.”

The Colorado River needs sediment. It builds beaches in the Grand Canyon, creates habitat and carries nutrients downstream. Some of the material now trapped in Lake Powell would eventually have made its way toward the Gulf of California in Mexico. “This is an unmanaged byproduct,” DeHoff says, of the mountains of mud we pass by.

That raises a question that is becoming harder to avoid as Lake Powell shrinks: How could all this mud be managed better? One option would be to keep using Glen Canyon Dam as a giant sediment trap, even as the reservoir behind it shrinks. DeHoff thinks that would repeat the mistake that created the problem in the first place. “Even in the face of Lake Powell going away, some people may choose Glen Canyon Dam to be the giant mud stopper,” he said.

DeHoff’s preferred approach is simpler, at least in principle: manage the Colorado as a river, not just as a plumbing system, “and let the sediment flow,” bypassing Glen Canyon Dam in the process. “But that really only works if you drain Lake Powell,” said Anne Castle, former federal representative to the Upper Colorado River Commission.

Castle has been on two Returning Rapids policy excursions to Cataract Canyon. Glen Canyon Dam was simply not built for the conditions the river is experiencing now, she said. As warming temperatures sap snow in the river’s headwaters, she said officials should look closely at whether Lake Powell’s continued operation is still a wise choice. Closing it would eliminate hydropower production and storage that helps meet the drinking water demands of tens of millions of people. Lake Powell’s storage capacity is currently key to long-standing water agreements among the U.S. states that rely on the Colorado River. But “the situation that we're facing now requires us to re-examine some of our assumptions and how we can best use the infrastructure with the river we have today,” Castle said.

The current federal administration is not ready to contemplate that future. It recently released a new Colorado River management plan, and it focuses on retaining as much water as possible in Powell. Federal officials haven’t done high-flow releases from Glen Canyon Dam since 2023, which are designed to help rebuild the Grand Canyon’s languishing beaches.

If snowpack continues to dwindle in the river’s headwaters like climate models predict it will, more mud will be exposed and sent into the reservoir. The exact shape of that future will depend partly on how much water arrives from melting mountain snowpack and partly on how the river is managed. After a record-setting hot and dry summer, all attention is on what this upcoming winter will bring. A super-charged El Niño is inflating hopes of a Lake Powell revival. But the volumes of water needed to refill it would take years of sustained change, not just one wet winter.

A dry year would turn the screws on policymakers even further and force tough choices on how the region’s scarce water is divided and used. “So either way, I think the river is going to win,” DeHoff said. “And we get to have front row seats to watch what’s going on.”

By the time Johnson crested the ridge of crumbling Lake Powell sediments, a line of mud reached well past her ankles. Fine sediments—eroded from the Rocky Mountains, transported here by a river, and then trapped by a reservoir and dam—coated her face and hands.

Lately, she’s started thinking about how this strange sedimentary blip in Earth’s history might show up in the geologic record. If a geologist ten million years from now stumbled upon a layer of Lake Powell sediments, would they know what happened? Could they figure out exactly what they’re looking at?

“It's this new geologic era record right there in front of me,” Johnson said. “I just can't ever get over that. It's a bit like the Rosetta Stone in a way, and we can really learn a lot from it.”