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. 3 . METHODS . The study area was the Green River from Jensen, Utah, to Green River, Utah, a distance of 175 miles (Figure l). The area from Jensen to Sand Wash was sampled from August 5 to August 20, 1977, and the area Sand Wash to Green River (Desolation and Gray canyons) on September 7- 14 and 22-26, 1977. The primary objective (#1) of the study was to determine the physical and chemical parameters of the habitats of the rare fishes. This was accomplished by sampling fish in the various habi- tats present, using boats from Jensen to Sand Wash and a rubber raft from Sand Wash to Green River. Velocity, depth, temperature, and substrate type were also measured in each habitat sampled for fish. Habitats were categorized as back- waters, eddies, runs, and riffles. Current velocity was measured in the part of the habitat where velocity was most representative of that area. A Marsh-McBirney model 201 portable water current meter was used to mea- sure velocity to the nearest 0.1 foot per second. Maximum depth of the area was recorded to the nearest inch using a graduated wading rod. Sub- strate type was recorded as silt, sand, gravel, or cobble, or combinations and was evaluated visually. The silt category was subdivided into soft silt when it clogged the seine and firm silt when it did not clog the seine. Temperatures were taken with hand-held pocket thermometers and electronic temperature instruments (Yellow Springs Instrument 02 and con- ductivity meters). Other salient features of the habitat were noted. In addition, a sketch of the river in the vicinity of the sample was drawn . . . . . . . .