Glen Canyon Dam has created a world of mud

By Dave Marston

When the San Juan River flows out of the San Juan Mountains in Southwestern Colorado, it contributes 15% of Lake Powell’s water.

But there’s a problem: The river carries a hefty 55% of the sediment entering the reservoir, and that mud is piling up.

The sediment-heavy river flows south into New Mexico before jogging into Utah, then it joins the Colorado River close to the Arizona border. The confluence is submerged under Lake Powell.

After decades of drought, the reservoir created by Glen Canyon Dam has dwindled to just a third full. Now, as the San Juan River flows toward Lake Powell, it rambles over a huge pancake of mud that’s 49 miles long, a mile wide in some places, and as much as 120 feet deep in the final reaches of the San Juan River.

Unique hydrology has contributed to this plug, A relatively wide canyon and multiple waterfalls slow down the river, allowing sediment to drop out. Though the San Juan is the muddiest tributary, all the Colorado’s tributaries drop a good deal of mud 100 miles or more upstream of Glen Canyon Dam.

It’s a Western phenomenon caused by damming swift rivers, said Jeff Geslin, a geologist at Fort Lewis College in Durango, Colorado. The result is that reservoirs in the West have become “temporary sediment storage facilities.”

If that mud could move through the Grand Canyon, like it did before the dam, biologists say that would help restore the canyon’s ecosystem, which depends on sediment-laden flushes in spring to scour riverbanks. Then, as the river slows, beaches form and vegetation returns.

Gary Gianniny, professor of Geosciences at Fort Lewis College in Durango, Colorado has been studying the San Juan River, along with river researchers who call their team, “The Returning Rapids Project.”

The group’s big worry is that without drastic action—draining Lake Powell to let the Colorado River run free—time may be running out for the languorous San Juan River.

Mike DeHoff, principal investigator of the Returning Rapids Project said the sediment layer on the San Juan has created new channels and new waterfalls. DeHoff added that no one knows whether the river’s sediment plug would dissipate even if Glen Canyon Dam were breached.

Researchers boating the San Juan River where it approaches Lake Powell say they’re forced to navigate an ever-moving pile of sediment that also involves portaging around rock waterfalls. When they finally arrive at Lake Powell, there’s dangerous liquefied clay and sand to navigate.

“I’ve seen people sink to their chests in the mud, saved only by their flotation devices and nearby boaters,” said DeHoff of Moab, Utah.

“We’ll need a drone to study that area,” added Gianniny.

Researchers with the Returning Rapids Project talk a lot about what to call these giant slabs of calving sediment. DeHoff suggests “mud bergs.”  

Semi-solid mud walls along the river have already been dubbed “the Dominy Formation,” named after the avid federal dam-builder Floyd Dominy.

“Technically, Gianniny said, the giant mud plug is a “mass of uncompacted mud and sand that causes alluvial fanning.” And falling slabs of sediment, those “mud bergs,” act as semi-permanent river features.

BLM River Ranger Chad Niehaus uses a packraft to regularly visit what researchers are calling the Lowest San Juan. He floats over 30-plus miles of the muddy river, finishing with a four-mile backpack out to a four-wheel drive vehicle 48 miles from Page, Arizona as the crow flies.

Niehaus marvels at the deserted region. “Sediment is moving around, and you must be vigilant in a different way than you do on a ‘normal’ river.”

Drought, climate change, “whatever you call it, the Lowest San Juan has re-emerged,” Niehaus said about wildlife in the once-submerged canyon. “I’ve seen river otters, mountain lions, coyotes—even pelicans—but the most astounding aspect is how quickly nature is coming back.” In places, cottonwood trees are 20 feet high, he said.

“When I was a teenager there were places on maps that were considered forever gone,” he said, pointing to sections on the map entitled, “Glen Canyon National Recreation Area.”

Now, he said, “some forever-gone places are revealed.” He mentions Cathedral in the Desert, a wondrous site on the nearby Escalante River. Enough water has receded to make it visible, though some of this sacred place for Indigenous people is buried under 30-plus feet of sediment.

Meanwhile, the muddy end of the San Juan River is wild again: “I rarely see a footprint.”

Dave Marston is the publisher of the independent nonprofit, Writers on the Range,, dedicated to spurring lively conversation about the West. He lives in Durango, Colorado.

Calving sediment below Clay Hills, UT San Juan River, courtesy Chad Niehaus

This column was published in the following newspapers:

03/04/2024 Salt Lake Tribune Salt Lake City UT
03/05/2024 Grand Junction Daily Sentinel Grand Junction CO
03/05/2024 Four Points Press Garryowen MT
03/05/2024 Glenwood Post Independent Glenwood Springs CO
03/05/2024 Colorado Free Press Denver CO
03/05/2024 Vail Daily Vail CO
03/07/2024 Cochise County Herald Review Cochise County AZ
03/07/2024 Craig Daily Press Craig co
03/07/2024 Aspen Daily News Aspen CO
03/06/2024 Denver Post Denver CO
03/05/2024 Taos News Taos NM
03/07/2024 Montrose Daily Press Montrose CO
03/07/2024 Durango Herald Durango CO
03/07/2024 Big Pivots Denver CO
03/08/2024 Laramie Boomerang Laramie WY
03/07/2024 Pagosa Springs Sun Pagosa Springs CO
03/07/2024 Durango Telegraph Durango CO
03/09/2024 Carlsbad Current-Argus Carsbad NM
03/09/2024 Farmington Daily Times Farmington NM
03/09/2024 Las Cruces Bulletin Las cruces NM
03/09/2024 Yahoo sunnyvale ca
03/13/2024 KVNF Radio Paonia CO
03/13/2024 Jackson Hole News & Guide Jackson Hole WY
03/08/2024 Kingman Daily Miner Kingman AZ
03/15/2024 Lake Powell Chronicle Page AZ
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Hal Jaeke
1 month ago

Great article. Glad there are researchers looking into this long term issue.

Tom Ribe
1 month ago

The source of much of the mud is overgrazed public land. When cattle denude the land, sheet erosion occurs and the sediments join the river. We need to look critically at grazing on public lands as drought deepens.

Eric Smith
1 month ago

I guess I have a couple of questions about the San Juan that might help steer us towards solutions. Has it always been muddy? What was the San Juan like between the mountains and the “true” confluence with the Colorado before Lake Powell was built? If the amount of sediment in the San Juan prior to Lake Powell was less, then what are the sources of the sediment load now? Tom Ribe puts forward one possible source. I would suggest another source was the wholesale removal of beavers and their engineered ponds, wetlands and meadows from not just the San Juan but also all the tributaries that contribute flow to the San Juan watershed. Now, it is true, the extirpation of beavers within the San Juan watershed was long before Lake Powell was built. But considering how much sediment a beaver dam and floodplain can impound, it might be worth looking at reintroducing beavers and/or building a number of Beaver Dam Analogues (BDA’s) to reduce the amount of sediment reaching the San Juan Mud Berg. Just a thought.

Russ Bessette
23 days ago

Sand waves in the San Juan are a phenomenon I haven’t experienced in other rivers. The sediment seems to have created more hangups and boat pulling recently than in the past. My last trip was considerably more difficult than the previous year.

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