As Lake Mead Sinks, States Agree to More Drastic Water Cuts

Three years ago, state hydrologists in the Colorado River Basin began to do some modeling to see what the future of Lake Mead — the West’s largest reservoir — might look like. If the dry conditions continued, elevations in Lake Mead, which is fed by the Colorado River, could drop much faster than previous models predicted.

For decades, the West’s big reservoirs were like a security blanket, says Anne Castle, the former assistant secretary for water and science at the Interior Department. But the blanket is wearing thin. Under normal conditions, Lake Mead loses 1.2 million acre-feet of water every year to evaporation and deliveries to the Lower Basin states plus Mexico, which amounts to a 12-foot drop.