Effects of Glen Canyon Dam on the Colorado River

"The River Is Forever Changed"

Overview

By changing the flow of the Colorado River, Glen Canyon Dam has changed the entire ecosystem downstream.

The system now contains a mixture of native and non-native plant and animal communities that began developing prior to the dam with the introduction of non-native fish and vegetation.

Dam construction and operation further modified this mixture by changing the physical conditions that affect vegetation and wildlife.

Some of the elements of the Grand Canyon ecosystem that have been altered by Glen Canyon Dam are

• Water
• Sediment
• Native and non-native fish
• Riparian vegetation
• Native American cultural and archeological sites

A Mixed Blessing

"Glen Canyon Dam has proven to be a mixed blessing for the Grand Canyon."
--Larry Stevens, in "The Colorado River in Grand Canyon--A Guide"

Some positive effects of the dam are power generation, expanded and more diverse wildlife habitats, and improved recreation. Non-native trout have thrived in the clear, cool water released from the dam, turning Lees Ferry into one of the finest trout fishing sites in the Southwest. The same water delights thousands of river runners annually, most of whom would not be attracted to the river before the dam--in Stevens' words, ". . .a sea of churning mud, a memorable but uninviting spectacle in flood and a trickle during dry years."

Some negative impacts of the dam are the loss of camping beaches, the decline of native fish populations, and the loss of the inundated parts of Glen Canyon. The mix of positive and negative changes brought about by Glen Canyon Dam make it more complicated than one might expect to answer the question posed by Glen Canyon Environmental Studies: "Are there ways to operate the dam . . . that would protect or enhance the environmental and recreational resources?"

Can Controlled Floods Help Restore Natural Resources?

A controlled flood was held in late March and early April of 1996, and again in November 2004, to help researchers determine if periodic large releases from Glen Canyon Dam can help restore some of the resources and dynamics of a natural river system.

See Suggestions for further reading for the sources of information on this page.