San Luis Rio Colorado, Mexico — Under the red girders of a nondescript toll bridge, waves gently lapped coarse sands in a gritty corner of this northwestern Mexican border city.

“There is usually no water and vegetation, and the ground looks like this,” local conservationist Alejandra Calvo-Fonesca said, gesturing toward the dusty shoreline of the Colorado River.

For a few months this winter, residents welcomed an unexpected surge of water in the river – a phenomenon they had not experienced since the spring 2014 “pulse flow,” when the United States released 107,000 acre-feet of water into the Colorado River Delta over a two-month period. That seminal event brought revelers in droves, eager to celebrate the revival of a historic waterway that is not only the city’s namesake, but a source of pride for its people.