Dams Still Shape the Colorado and Green Rivers in Canyonlands

The Green River in Canyonlands National Park. NPS / Amy Washuta.

Many communities in the western United States get their water from the Upper Colorado River Basin, which is also home to many native plants and animals. The Green River, a tributary of the Colorado, is an important part of this system. This page draws on a "Research Roundup" item in the National Park Service's Park Science magazine (Winter 2024–25).

What the dams changed

Dams completed in the 1960s altered the natural flows of the Colorado and Green rivers. More plants took hold along the riverbanks, and the river channels narrowed. Since 1992, water has been released from the dams to restore more natural flows and protect native fish.

The study

Researchers used images taken from aircraft and satellites to study vegetation along the rivers in Canyonlands National Park, comparing the period before the dams, the period after them, and the years of environmental releases. Their findings, published in River Research and Applications in October 2024:

• Since 1940, plant growth along the rivers has increased significantly.
• Over the last 16 years, the spread of plants has slowed, suggesting that channel narrowing has slowed too.

Slowed, not reversed

The authors concluded that the environmental releases, together with a large spring flood in 2011, have slowed but not reversed the dams' effects — partly because less water is flowing into the rivers and more is being diverted. Large periodic peak flows combined with environmental releases are essential to keep the channels from narrowing.

Sources

• National Park Service, Park Science 39(1), Winter 2024–25: "Vegetation Study Shows Colorado and Green Rivers Face Ongoing Challenges," by the editors of Park Science.
• Perkins and others. 2024. "Riparian Vegetated Area in Pre-Dam, Post-Dam, and Environmental Flow Periods in Canyonlands National Park From 1940 to 2022." River Research and Applications.