Sometime between 11 and noon on Sunday, the water level in Lake Mead, the massive reservoir whose water fills the taps of millions of people across the Southwest, fell lower than it ever has since it was filled 75 years ago.
Even as a flurry of thunderstorms dropped rain on the Las Vegas area, with as much as an inch falling in the mountains to the north, Lake Mead’s level dropped to 1,083.18 feet above sea level just before noon, and fell further, to 1,083.09, by 9 local time Monday morning. (The Bureau of Reclamation site features a bar graph showing the reservoir levels since the lake was first formed when the Colorado River waters were impounded by Hoover Dam.)
“It is a record-setting moment,” said Colleen Dwyer, a spokeswoman for the Bureau of Reclamation. She added that slightly more water than usual had been released through Hoover Dam over the weekend because the power marketing agency that sends dam-generated electricity around the Southwest had requested some additional flow.
Lake Mead’s levels are still eight feet above the level at which a shortage is officially declared and limited rationing could go into effect for users in Nevada and Arizona, and well above the levels when the Hoover Dam’s hydroelectric output might be seriously jeopardized.
But Barry Nelson, a senior policy analyst for the Natural Resources Defense Council, said: “This strikes me as such an amazing moment. It’s three-quarters of a century since they filled it. And at the three-quarter-century mark, the world has changed.”
He noted that Hoover Dam was “one of the iconic features of American engineering” and one of the earliest of what are now 45,000 major dams on rivers worldwide. “This is the place where the mega-dam began, and it may be the place where it ends,” he said, because of “climate change and new constraints on water supplies.”
Mr. Nelson said that the 11-year drought, which has caused the Colorado River to deliver considerably less water than its users have been promised, “reflects weather patterns that are what climate models predict for an era of climate change.”
“Either these are early indicators of climate change or conditions we should expect more of in the future,” he concludes.
The Bureau of Reclamation’s current plan for the coming year calls for an increase of up to 40 percent in the amount of water delivered to Lake Mead from Lake Powell, the big reservoir upstream, a step that could help equalize the amount of water in each reservoir and possibly avoid triggering the shortage declaration.