In the arid region south of Mexicali, where the pale desert dominates the landscape, the Las Arenitas wetland feels like a mirage. But it is real, and is an oasis for endemic and migratory birds that cross the Colorado River delta. Here, just south of the US-Mexico border, used water from the city of Mexicali gets a second life. Half of it goes to the nearby Hardy River, in an attempt to revive ecosystems that were thought to be irrecoverable.
Historically, waterways here have been flushed full of sewage—particularly the New River, which runs off from the Colorado River northwards, crossing from Mexico into the United States and ending in