The Colorado River comes to an end at the U.S.-Mexico border. The entirety of its flow, already heavily tapped upstream in the U.S., is sent into an irrigation canal to grow crops in the Mexicali Valley and to flow through faucets in Tijuana and Mexicali. The river’s final hundred miles have been mostly dry for decades. Environmental groups on both sides of the border are working together to let the Colorado flow again in its historic channel.