Once upon a time, the Colorado River Delta — a plain the size of Rhode Island — supported a dazzling number of plant and animal species, and its annual flood cycles brought fresh nutrients to the delta. Today the Colorado is one of the most intensively managed rivers in the world, supplying water or electricity to 30 million people. The upshot? In the course of one generation, the delta has gone from a verdant wilderness to nearly a dry land. Most of the wildlife it used to support is gone, and communities that lived by fishing its waters or farming near its banks are dispersing. Now U.S. and Mexican environmentalists hope to change that by suing the U.S. Department of the Interior to reserve a portion of the river’s water rights for nature. (Right now, the river’s entire water supply is divvied up between seven U.S. states and Mexico.) If successful, the suit would essentially broaden the U.S. Endangered Species Act to include threatened habitats in areas abutting U.S. lands.