CNN —Lake Powell, the second-largest human-made reservoir in the US, has lost nearly 7% of its potential storage capacity since 1963, when Glen Canyon Dam was built, a new report shows. The capacity of the reservoir is shrinking because of sediments flowing in from the Colorado and San Juan rivers, according to the report. As of Monday, Lake Powell was around 25% full, according to data from the Bureau of Reclamation. 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.