A dozen miles from Lake Powell, up the Dirty Devil River, our canoes enter the old lake-bottom layer. Dirt banks rise above our heads, and the turbid river churns through an alley bounded by sand walls. Bend by tight bend we cut deeper into the canyon of fine sands. On top, a fringe of tamarisk as thick as fur rims the edge. These layers of fine silt drifted to the bottom of Lake Powell when the reservoir was at full pool, and it has been decades since the water was that high. It feels chilly and strange in the tunnel of dirt. It is late afternoon and there are no places to camp.

For more than four days, and some 75 miles, we have floated the shallow currents of the Dirty Devil. The floatable window on this seasonal stream has been cut to two weeks in late March. Before that, it's too cold for any runoff. After that, upstream irrigation demands slow the flow to a trickle. Our timing was right, but we still had to get out and wade repeatedly for the first day and a half.

The payoff is miles of sandstone-rimmed canyon twisting through remote high desert in central Utah. Think Butch Cassidy's old stomping grounds, slot canyons with sheer, fluted, water-worn walls, and places like Happy Canyon, where we walked for miles through an aisle of rock an arm's width across. Then there are the cottonwood bottoms amber with sunlight, tributaries to explore every few miles. There's no human company, no bureaucracy; just night skies stuffed with starlight. As Butch discovered, it's a sweet place to escape civilization.

But now this: The walls build and a mild case of claustrophobia infects us. At twilight we find a toe of dried mud big enough to pull up our boats onto and pitch a tent. It's like we found the only motel in town with a vacancy sign. We take it. All night, when I wake, I smell mud. The river slides past, working towards a new equilibrium, slicing through this weird layer cake.

When morning sun hits our camp, we are ready to leave. The boats push on through the gantlet of sediment, around 90-degree turns tugging us to the end of our trip at Hite Marina on Lake Powell. Overhead, sandstone walls remind us of a landscape free of silt.

Around mid-morning, the high bridge where Highway 95 crosses the Dirty Devil rises above us. A few more turns, and there's the flat sheen of shallow lake. There is still a current, but it spreads in a broad skirt, blending into the artificial basin, burying dozens of canyons like the Dirty Devil. It is more and more difficult to pick out the deepest channel. A western grebe glides across the flats, one red eye trained on us. Truncated sandstone buttes poke out of the lake.

The current dies as the "river" becomes only inches deep. With every stroke I feel the quicksand beneath the hull. Bottomless muck, it stinks like primordial ooze, like methane, and if we step out, my guess is that we'll sink in it up to our necks. For a stretch we paddle through what amounts to the bathtub ring, a rainbow sheen of petroleum that slicks the surface as bits of Styrofoam, clods of suds, candy wrappers all jostle in our wakes.

This lake that has become a failing reservoir was sold to us back in the 1960s as a great idea. Back in that era of technologic seduction, the age of the interstate highway and the space program, we believed that a dam could do everything, including flood control, recreation, hydroelectric power and jobs. Almost half a century later, with the lake filling with mud, canyons buried or backed up, and an atrocity of evaporation lying under the sun, it doesn't feel so spiffy.

John Wesley Powell floated past here on July 28, 1869. One of his men dubbed this tributary "a dirty devil of a river." The name stuck. They had just survived the drubbing of Cataract Canyon. They floated on the eddying currents of the Colorado, recovering, wondering what was next, with no idea that the Grand Canyon was coming right at them.

The water gets deeper. I stop worrying about drowning in mud. We slog across the flat pond, make our way to the obscure boat ramp at Hite. It has become obscure because the boat ramp is several hundred yards short of the water. For us, that means crossing several hundreds yards of shoe-sucking, putrid ooze as we portage everything to our car.

We load up and drive away quickly, clinging to the memories of Happy Canyon and all the other canyons back upstream of this insult, this filthy bathtub that someone thought was such a good idea 50 years ago.

Alan Kesselheim is a contributor to Writers on the Range, a service of High Country News (hcn.org). He writes in Bozeman, Montana.