Until recently, most believed that silt was collecting mainly where rivers enter the reservoir. (Currently, the Colorado River has deposited material 150 feet deep where it slows around Hite Marina, rendering it inoperable.) But underwater mapping reveals that the majority of infilling is happening in the reservoir's center. As a result, Lake Powell might fill more quickly and thoroughly than expected, another variable to figure into the many equations.

Back on the surface, the water takes on an emerald tone. White-washed boulders alongshore reflect light off the water while mouth-sucking carp splash on the surface. Sometimes, the only evidence of the river is the yawning shape of a canyon the San Juan left behind. But then I notice a downstream-trend to floating debris, plastic water bottles and oil cans all heading the same direction. Methane bubbles rise from organic decomposition in the sediment below, and the slow current moves the bubbles into trains.

As I paddle into the afternoon, a stiff wind strikes -- 40 mile-per-hour gusts kicking up chop as I fight my way across the reservoir. Eventually, I come into the remnants of the old Glen Canyon, big domes of Navajo sandstone melting into each other, dark springs and seeps sheeting from seams in the rock. Side canyons lean back into enormous alcoves, places that once towered high over the river and are now at eye-level.

In the open expanse, shelters become few for miles at a time. Wind creates standing waves and sheets of mist, giving the reservoir a last illusion of movement.

The next day I hunt diligently for a current, zigzagging across flat water. When afternoon winds come up, I put my head down and paddle straight, forgetting about the river.

By evening, the wind settles a bit. I search for the river a last time, but cannot find it. It is now a ghost sliding along the bottom of Lake Powell. I pull the banana onto a sandstone bench; water clear enough to see a rock face descending sharply. It is a cliff dropping off, but I can only see the top several feet before it falls into greenish shadow.

Here, I make camp, setting my bag among big linen blooms of datura. The water gulps against cliffs, and canyon tree-frogs call loudly from a spring across the way. The channel is hardly wide enough to call a lake. It still looks like a river. In fact, all of Lake Powell looks more riverine than the typical pool-shaped bodies we know as reservoirs. Its 2,000-mile shoreline (more waterfront than the entire Eastern Seaboard) consists of narrows and meanders, each the shape of the river and canyons it possesses.

I have a friend named Katie Lee, now 91, a longtime defender of free rivers and a fist-pounding enemy of Glen Canyon Dam. She knew these rivers before they were dammed, and she still cries over the loss. She once spread maps and photos across her living room floor and told me stories of wonderful places now drowned. She is the one who first told me that you cannot kill a river. She felt as if her rivers were gone when the dams went in, but she knew that they would not truly be stopped, that they would still obey the most intrinsic of laws, continuing to run downhill dammed or not. What looks static is actually in motion, still water deceptively reworking itself, and the landscape it passes through. There is a heartbeat down there at the bottom.

That night, sitting in the crease of the San Juan's canyon quarter-filled with lake water, I pull out my journal. The top of each preceding page had been titled, "Lower San Juan." Starting the next page under a headlamp, I hesitate, go to the top, and finally pen, "Lake Powell."

Related: an animation of dropping water levels in Lake Powell, from NASA.

This story was made possible with support from the Kenney Brothers Foundation.

Craig Childs writes from near Crawford, Colorado, where he adds to sediment coming down the Gunnison River. He is this year’s winner of the Ellen Meloy Desert Writers Award, and he has authored several books. His work has appeared in the New York Times, Men’s Journal, Orion and The Sun.