Panorama of Glen Canyon Dam and downstream Colorado River (photo from Wikimedia Commons)

14 August 2025

After 25 years of drought in the Colorado River Basin the water levels at two major dams — Glen Canyon and Hoover — are getting dangerously low.

Map of Colorado River Basin indicating Glen Canyon and Hoover Dams (map from Wikimedia Commons)

Here’s the bathtub ring at Lake Powell as seen in March 2025 at the Glen Canyon Dam …

“Bathtub ring” at Lake Powell as seen from the Glen Canyon Dam, March 2025 (photo from Wikimedia Commons)

… and the bathtub ring at Lake Mead as seen in August 2024 at Hoover Dam.

“Bathub ring” on Lake Mead at Hoover Dam, August 2024 (photo from Wikimedia Commons)

Hydrologists are now talking about the possibility of “dead pool” at one of these dams. What is dead pool and what does it mean for the river?

The Glen Canyon Dam, completed in 1966, was designed for the relatively abundant water of the 1950s. The dam crest is more than 3,700 feet above sea level with two sets of pipes for water to pass through the dam: the hydropower intake at 3,490 feet for generating electricity, and the river bypass at 3,370 feet that sends water straight through the dam. This diagram from the Grand Canyon Trust shows how the dam works.

diagram of Glen Canyon Dam water levels from Grand Canyon Trust

They didn’t think about a drought. If Lake Powell’s surface falls below 3,370 feet there’s no way water can get through the dam. That’s called dead pool and it means the downstream river is dry.

This 4-minute video from Arizona’s 3TV CBS explains what will happen.

Ironically, this means the Glen Canyon Dam’s useful life was only 60 years.