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At RM 343.0 (km 549) the Green River abruptly enters Whirlpool Canyon. This statum (G ) is characterized by boulder/bedrock substrate and near-vertical cliffs. Habitats are primarily deep eddies, rapids, riffles, and large pools. Significant deposits of sand are present?in some large eddies, and backwaters and isolated pools occur in these areas when the river level drops. River gradient in this stratum averaged 11.1 ft/mi. A perennial tributary, Jones Hole Creek, enters at RM 338.6" (km 542). Except during runoff, turbidity is very low; postrunoff average was 26 FTU's. Stratum G2 extended from RM 334.0 (km 534) downstream to RM 327.0 (km 523). The Green River in this stratum meanders through cottonwood-- lined sand/cobble shorelines in Island Park and Rainbow Park. Gradient is the least of any of the four Green River strata, 3.4 ft/mi. The river is shallow (average depth 3.5 ft during runoff and only 2.0 ft during postrunoff) and contains many side channels and isolated pools,` depending on water level. Stratum G1, Split Mountain Canyon, extended from RM 327.0 (km 523) to RM 319.0 (km 510). During its passage through Split Mountain, the Green River flows through several large boulder fields which create four. major rapids. Average gradient in the stratum is 18.6 ft/mi and hab- itats are mostly rapids, riffles, and eddies. Substrates are primarily boulder and rubble, with some large sand bars formed in areas of de- creased water velocity. Little Snake River The Little Snake River was not treated as a distinct stratum., however, surveys were conducted in the lower 9 mi (14.4 km). The Little Snake River is the major tributary to the Yampa River, and strongly, influences fishery habitat downstream of its confluence. The lower 9 mi (14.4 km) of the Little Snake River pass through cottonwood and sagebrush communities. Some minor riffle areas occur at low water levels, but the river is generally broad and shallow with sand/ silt substates predominating. Gradient is low, and current velocities are low except for a few areas where the channel cuts through rock outcroppings. The Little Snake River transports a lot of sediment in the spring which, along with the additional water flow, dominates the Yampa River for several miles below its confluence. Distribution and Relative Abundance of all Fish Species A total of 24 species representing nine families was collected in the Green (19 species), Yampa (24 species), and Little Snake (11 spe- cies) rivers in 1981 including all sampling programs (Table 5). Eighteen species were common to both the Green and Yampa. All eleven species found in the Little Snake River were also collected in both the Yampa and Green rivers. Razorback sucker (Xyraucheri texanus) was collected in 26