Fish populations in the Green and Yampa rivers have undergone significant changes in the last century. Today, more than 50 fish species can be found in these rivers, but fewer than a third of those are native to the Green and Yampa. Of the 14 native fish species, four are endangered--the razorback sucker, humpback chub, Colorado pikeminnow, and bonytail--and others are declining.

Fish native to the Green and Yampa evolved in natural-flowing rivers whose water was often clouded by dirt, silt, and other sediments that washed in from the surrounding countryside; in rivers with high spring flows fed by snow melt; and in rivers where water temperatures could range from near freezing in winter to almost 70F (21C) in summer.

In 1962, with the construction of Flaming Gorge Dam, these conditions largely disappeared from the Green River. Spring flows, temperature fluctuation, and turbidity (the cloudiness of the water) were all reduced. The Green River downstream from the dam became a much clearer, cooler, and calmer river. These changes reduced the number and distribution of several native fish, all of whom were adapted to the rugged conditions of the undammed Green River. Many of these changes in the river system also created more favorable conditions for non-native fishes.

Over the last century, a number of fish species have been added to the Upper Colorado River Basin. Some of these non-native fish were introduced by state and federal agencies to meet sport-fishing demand that existed at the time. Other species were unintentionally introduced when they escaped from ponds and reservoirs into the river system. Non-native fishes compete for resources including food, space, cover, and physical habitat, and are known to prey on native fishes.

The Yampa River, the largest unregulated tributary remaining in the Colorado River system, has played a vital role in sustaining these endangered fish species. Thanks to the Yampa's near-natural annual flows, Dinosaur NM provides some of the last known spawning and nursery habitat for several of these big river species. Because it mitigates the effects of Flaming Gorge Dam, the Yampa River also improves the ecological integrity of the Green River after the two rivers join at Echo Park.

Credits and Sources:

“Endangered Fish,” National Park Service, http://www.nps.gov/dino/learn/nature/endangered-fish.htm (accessed 15 June 2015).