Relentless drought will force the government to cut back on water releases between Glen Canyon and Lake Mead on the Colorado River, threatening water supply for Arizona and the other lower basin states, the U.S. Bureau of Reclamation reported Friday.

It's the first time that's happened since dams were built on the Colorado River. Reduction will start next year, and the announcement gives the 40 million water users in the Southwest time to plan.

Water shortages could begin as early as 2016, National Public Radio's Ted Robbins reports: