The Green River basin is the last remaining stronghold of the Colorado squawfish (Ptychocheilus lucius) and the razorback sucher (Xyrauchen texanus) in native riverine environments. It also supports populations of the humpback chub (Gila cypha) and is a recommended recovery area for the bonytail chub (Gila elegans). Flows of the Yampa River, last free-flowing river containing endangered fish habitat in the Upper Colorado River Basin, are considered critical to the maintenance of usable fish habitat of rare and endangered fishes (Figure 1) in the Green River basin (reviewed by Tyus and Karp 1989).
