The federal Bureau of Reclamation runs both dams and sets their releases. Its Aug. 21 rules for 2027–28 limit Lake Powell’s releases to 6–7 million acre-feet a year, aiming to hold it at 3,510 ft or higher, and cut what Arizona, California and Nevada take from Lake Mead by 1.25 million acre-feet a year to slow its drain.
Hoover Dam: down 43% since 2001
Danger zone: below 1,035 ft. 12 of Hoover's 17 turbines go offline and capacity drops 70%; at 950 ft, power stops. Lake Mead is 2.65 ft above the zone and expected to enter it by year's end.
Annual net generation, 2001–2025 (TWh)
Chance Mead stays above 975 ft, 2027–39
Current operations54%
New rules72%
Glen Canyon Dam: down 28% since 2001
Danger zone: below 3,500 ft. At 3,490 ft all 8 turbines stop and water can leave only through bypass tubes, risking the dam's reliability. Lake Powell is 19 ft above the zone.
Annual net generation, 2001–2025 (TWh)
Chance Powell stays out of the danger zone, 2027–39
Current operations30%
New rules58%
Source: EIA Form EIA-923 (Hoover: Nevada + Arizona combined). U.S. Dept. of the Interior, 2027–2028 Operating Guidelines, Aug. 21, 2026. U.S. Bureau of Reclamation: lake levels and Sept. 24-Month Study forecast, Oct. 12, 2026; Post-2026 Colorado River Final EIS, July 2026, Figs. 3-9 and 3-11 (share of 400 modeled futures). The Water Desk, June 2026.