Come spring, the American West’s vast water reservoirs are supposed to fill with melting snow. However, this year, as in recent years, the large reservoirs of Lake Mead and Lake Powell in the Colorado River basin area have seen declining water levels — an ominous trend that a new study warns could signal a looming megadrought.

“The persistence of the drought conditions, in the Colorado River basin especially, is essentially unprecedented in human history,” John Fleck, author of “Water is for Fighting Over,” told CBS News’ John Blackstone.

Fleck has spent years studying the Colorado River, a crucial source of water for much of the region around it. He said that Lake Mead and Lake Powell’s reservoirs have what he described as “big bathtub rings” around them, left behind as the water declines.

“There is less water in the system…