Page, Ariz. — Lake Powell's Storage Capacity Has Shrunk 7% Since 1963

Lake Powell, the second-largest human-made reservoir in the United States, has lost nearly 7% of its total storage capacity since Glen Canyon Dam was completed in 1963, according to a report from the U.S. Geological Survey and the Bureau of Reclamation, cited by CNN. The finding means the reservoir's problem is bigger than a shrinking water level driven by drought. The reservoir itself can no longer hold as much water as it was built to hold.

What did the new report find?

The report found that Lake Powell lost an average of about 33,270 acre-feet of storage capacity per year between 1963 and 2018, according to CNN's account of the USGS and Bureau of Reclamation findings. That works out to roughly 11 billion gallons a year, or enough water to fill the Reflecting Pool on the National Mall about 1,600 times, CNN reported.

Why is the reservoir losing storage space?

Sediment is the cause, according to the report. Silt and dirt carried in by the Colorado and San Juan rivers settle at the bottom of the reservoir over time. That buildup takes up space that used to hold water, permanently reducing how much the reservoir can store even if rainfall and snowpack recover, the report found.

Lake Powell has lost nearly 7% of its potential storage capacity since Glen Canyon Dam was built in 1963, according to the USGS and Bureau of Reclamation report cited by CNN.

How full is Lake Powell right now?

As of the Monday before the report's release, Lake Powell was about 25% full, according to Bureau of Reclamation data cited by CNN. That level reflects the ongoing multiyear drought across the Colorado River basin, a separate factor from the sediment-driven capacity loss described in the report.

What does this mean for water users downstream?

The report does not spell out specific downstream cuts, but the combination of a shrinking reservoir footprint and a falling water level compounds the strain on a system that supplies water to millions of people and to agriculture across the Southwest. A reservoir that can hold less water to begin with has less room to recover even in wetter years, based on the mechanism the report describes.

Who produced the study, and where can residents read it?

The findings come from a joint report by the U.S. Geological Survey and the Bureau of Reclamation, the federal agency that operates Glen Canyon Dam and manages Colorado River reservoirs. CNN's report, which cites the federal findings and Bureau of Reclamation water-level data, is the original source for these figures; the full text is available in CNN's coverage.

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