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.

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

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

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.

The design engineers 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 about 60 years.