Climate security

U.S. largest reservoir drops to the lowest level in history

The nation’s largest reservoir has broken a record, declining to the lowest level since it was filled in the 1930s.

Lake Mead reached the all-time low Wednesday night, slipping below a previous record set in June 2015.

The downward march of the reservoir near Las Vegas reflects enormous strains on the over-allocated Colorado River. Its flows have decreased during 16 years of drought, and climate change is adding to the stresses on the river.

As the levels of Lake Mead continue to fall, the odds are increasing for the federal government to declare a shortage in 2018, a step that would trigger cutbacks in the amounts flowing from the reservoir to Arizona and Nevada. With that threshold looming, political pressures are building for California, Arizona and Nevada to reach an agreement to share in the cutbacks to avert an even more severe shortage.