Grand Canyon & Glen Canyon Dam: The Basics

The Canyon
Shaped by the Colorado River over the last six million years, Grand Canyon stretches 277 miles, is a mile deep and up to 18 miles wide. It was declared a National Park in 1919 and a World Heritage Site in 1979.

Cultural History
Human inhabitants of Grand Canyon have included sophisticated big-game hunters of the Clovis and Folsom cultures 10,000 years ago, Desert Archaic peoples from 6500 BC to 1 AD, and the farming culture of the Basketmaker and Puebloan peoples until about 1275 AD. Today, the Havasupai still live in Grand Canyon; the Navajo and Hualapai Nations have land in the Canyon, and the Canyon contains sacred sites revered by the Hopi and Zuni.

Dams and Grand Canyon
Hoover Dam flooded the lower 20 percent of Grand Canyon in 1941. Upstream, 15 miles above Grand Canyon, Glen Canyon Dam stopped the Colorado River's natural flow in 1963. In 1968, public opposition defeated proposals to build Marble and Bridge Canyon dams, which would have inundated much of Grand Canyon between Hoover and Glen Canyon dams.

Sediment and Nutrients
Ninety-five percent of Grand Canyon's sediment and nutrients are trapped behind Glen Canyon Dam. Organic materials mixed into this sediment used to provide the fertilizer for the river ecosystem's health. Instead, the Colorado River in Grand Canyon now runs clear and cold, allowing the green alga cladophora to grow and replace the natural warm-water food web. The absence of replenishing sediment is also causing critical beach and sandbar habitat to disappear, and undermining the stability of archaeological sites sacred to the Canyon's native peoples.

Truncated Habitat
The isolation of Grand Canyon's river habitat between Hoover Dam downstream and Glen Canyon Dam upstream has inhibited migration and genetic diversity among the native species still found in Grand Canyon.

Water Temperature
Today, water flowing through Glen Canyon Dam is extracted 200 feet below the surface of Lake Powell reservoir, too low for the sun's rays to penetrate. As a result, water entering Grand Canyon is a near constant 47°F. By contrast, before the dam was built, water temperatures ranged from near freezing in the winter to 80°F in the summer. These warm water temperatures were critical to triggering native fish reproduction and maintaining native insect populations.

Flows
Regulated flows currently keep the Colorado River in Grand Canyon fluctuating daily between 8,000 and 20,000 cubic feet per second (cfs). Before Glen Canyon Dam, flows in Grand Canyon fluctuated seasonally from 3,000 to 90,000 cfs. Spring snow melt brought a rushing torrent of water into the Canyon, transporting sediment, building beaches, replenishing the nutrient base on the river's shores and creating vital backwater habitat as the water receded. Low flows were critical for warming water, juvenile fish survival, and maintaining the food base.

Disappearing Species
River otters and muskrats are no longer found in Grand Canyon. Four of the eight native Colorado River fish are gone, and two more are struggling for survival. Native birds, lizards, frogs and many of the Canyon's native insects are disappearing as well. In addition, native vegetation along the river's high water zone is absent or stunted due to the lack of nutrients and the invasion of competing non-native plants species.

Designer Ecosystem
The river's altered chemistry, flow and temperature cycles have created an artificial environment allowing non-native species to dominate Grand Canyon's river corridor. Native plants and animals must now compete with new alien species for habitat and food. These changes run contrary to the mission of the National Park Service, which is to preserve the parks' natural integrity.

Legal Conflicts
Current management of Glen Canyon Dam runs counter to the intent of several federal laws, including: the Grand Canyon Protection Act, Endangered Species Act, Archaeological and Historic Preservation Act, and National Park Service Organic Act.

What's Needed
More than $100 million has been invested in failed efforts to reverse the demise of Grand Canyon's river ecosystem. Efforts will continue to fail unless all natural processes are restored: river flow, water temperature, and sediment and nutrient inputs. The simplest solution is to decommission Glen Canyon Dam.