Rowan Jacobsen, in the canoe, and Pete McBride and Sam Walton, on stand-up paddleboards, travel through the upper limitrophe of the Colorado River, along the U.S.-Mexico border. Before the release of water from the Morelos dam, Jacobsen described this parched riverbed as a trench, with big stretches of it bone-dry.
Jacobsen paddles through the Colorado River just above San Luis, Mexico, 17 miles below the Moreno dam. The release of water from the dam created a "pulse flow" that temporarily restored the river that used to flow here. Now, three months afterward, it's dry once more. In the absence of the river's flow, this region's native habitats have been replaced by invasive salt cedar.
An aerial view of the lower portion of the Colorado River shows the leading edge of the pulse flow before it connects with the sea. You can see the part of the delta the water has yet to reach in white, in the lower left-hand corner.
Before the water from the dam reached it, this area was dry sand: The water table is usually 30-40 feet deep in this region. The next two photos show this same spot as it experiences the changes wrought by the pulse flow.
Rowan Jacobsen's river trip stopped at this point, where — when they arrived — the flow of water had cut through the sand, but was a trickle too small for transportation. Here, Osvel Hinojosa checks in with his crew to tell them of the team's location, so they can bring in supplies.
Twelve hours after they had halted at the river's end, the team woke up to see that the previous night's small stream had become a river. Two weeks after this photo was taken, the leading edge of the water reached the estuary that was the river's final destination.