LAKE POWELL (KDVR) — Lake Powell, the second-largest constructed reservoir in the U.S., has lost almost 7% of its storage capacity since the Glen Canyon Dam was constructed nearly 60 years ago, according to a new report.

A report from the U.S. Geological Survey and the Bureau of Reclamation shows that Lake Powell lost 1,833,000 acre-feet, or 6.79% of its storage capacity at full pool. The reduction in storage capacity is attributed to sediment from the Colorado and San Juan rivers. Decreased storage capacity happened most frequently at elevations above 3,600 feet.

The recent report said the current storage capacity at full pool is 25,160,000 acre-feet. Both the USGS and the Bureau of Reclamation collected topobathymetric surveys starting in 2017 for the first update on the lake’s capacity since 1986.

“It is vitally important we have the best-available scientific information like this report to provide a clear understanding of water availability in Lake Powell as we plan for the future,” Assistant Secretary for Water and Science Tanya Trujillo said in a statement. “The Colorado River system faces multiple challenges, including the effects of a 22-year-long drought and the increased impacts of climate change.”

Lake Powell is currently down 42.98 feet from a year ago and is 23.87% of full pool. In March, the lake fell below the critical level of 3,525 feet above sea level, creating concern about hydropower-producing abilities. The last reading was 3,523.02, according to lakepowell.water-data.com.

Lake Powell is located on the Colorado River spanning Utah and Arizona. The Dam was built in 1963 to supply water to a growing southwest population.