According to a new analysis, Lake Powell, the US's second-largest man-made reservoir, has lost roughly 7% of its potential storage capacity since Glen Canyon Dam was erected in 1963.
Between 1963 and 2018, Lake Powell lost an average annual storage capacity of around 33,270 acre-feet, or 11 billion gallons, due to a multiyear drought, according to a report by the US Geological Survey and the Bureau of Reclamation.
That's enough water to fill the National Mall's Reflecting Pool 1,600 times.
According to the report, silt streaming in from the Colorado and San Juan rivers is reducing the reservoir's capacity. These sediments settle near the reservoir's bottom, reducing the total amount of water the reservoir can contain.
According to data from the Bureau of Reclamation, Lake Powell was roughly 25% full as of Monday.
It's bad news for a region already suffering from severe water shortages and wildfires as a result of the drought. Drought scientists from the National Oceanic and Atmospheric Administration stated this week that these circumstances are likely to persist, if not worsen, in the coming months.
In the Colorado River Basin, Lake Powell is a significant reservoir. Lake Powell and Lake Mead, the nation's largest reservoirs, have both been rapidly draining. After Lake Mead's water level plummeted to new lows, the federal government declared a water shortage on the Colorado River for the first time in August, initiating mandatory water-use limits for states in the Southwest that began in January.
Last Monday, Lake Powell fell below the key elevation of 3,525 feet above sea level, raising new fears about water supply and hydropower generation, which millions of people in the West rely on for power.
The importance of the Colorado River's diminishing water supply cannot be understated.
More than 40 million people in seven Western states and Mexico rely on the system for water. Many people in the region, including rural farms, ranches, and native villages, rely on Lakes Powell and Mead for drinking water and irrigation.
"It's critical that we have the best available scientific knowledge, such as this report, to offer a clear picture of water availability in Lake Powell as we plan for the future," said Tanya Trujillo, the US Department of Interior's assistant secretary for water and science. "The Colorado River system is dealing with a number of issues, including the effects of a 22-year drought and the growing effects of climate change."
