Lake Powell, the second largest human-made reservoir in the US, has lost a significant portion of its potential storage capacity since 1963, when Glen Canyon Dam was built, according to a new report.
The US Geological Survey and the Bureau of Reclamation found that Lake Powell had an average annual loss of 33,270 acre-feet, or 11 billion gallons, per year between 1963 and 2018 due to water loss due to an intense multiyear drought.
That is enough water to fill the Reflecting Pool on the National Mall about 1,600 times.
The report states that the reservoir's capacity is shrinking because of sediments flowing in from the Colorado and San Juan rivers. The sediments settle at the bottom of the reservoir and decrease the amount of water the reservoir can hold.
According to the Bureau of Reclamation, Lake Powell was about 25% full as of Monday.
It's bad news for a region already facing water shortages and extreme wildfires due to the drought. National Oceanic and Atmospheric Administration drought experts said last week these conditions are expected to worsen or continue in the coming months.
Lake Powell is an important reservoir in the Colorado River Basin. Both Lake Powell and nearby Lake Mead, the nation's largest reservoir, have drained at an alarming rate. In August, the federal government declared a water shortage on the Colorado River for the first time after Lake Mead's water level plunged to unprecedented lows, triggering mandatory water consumption cuts for states in the Southwest that began in January.
The lake Powell dropped below the critical threshold of 3,525 feet above sea level last week, sparking further concerns about water supply and hydropower generation millions of people in the West rely on for electricity.
The significance of the dwindling water supply along the Colorado can't be overstated.
More than 40 million people live in seven western states and Mexico, and the system provides water for the whole of the country. Lake Powell and Mead provide drinking water and irrigation for many in the region, including rural farms, ranches and native communities.
Tanya Trujillo, assistant secretary for water and science at the US Department of Interior, said in a statement that it is important to have the best-available scientific information like this report to provide a clear understanding of water availability in Lake Powell. The Colorado River system is facing multiple challenges, including the effects of a 22 year-long drought and the increased impacts of climate change.