An advocacy group is calling the Colorado River the nation's most endangered waterway.
An annual American Rivers report being released Wednesday doesn't call pollution the problem. It instead cites drought and demand.
The federal Bureau of Reclamation said the same thing last December.
The Colorado River supplies cities including Denver, Los Angeles, Las Vegas and Phoenix. The report says that over the next 50 years, the river will run short of supply for the more than 40 million people it serves in Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming.
Already, the river is drained of nearly every drop before it reaches Mexico.
The Flint River in Georgia ranks second in the American Rivers report, due to the threat that it'll run dry.
The San Salba River in Texas ranks third.