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Duchesne, Dolores, and Gunnison rivers (Figure 1). No actual size defi- nition has ever been attempted, to our knowledge, to determine if river size (cfs) is actually a requirement. Adults have been found in the mouths, or short distances upstream, of several small streams along the Green River during high runoff periods. The mouths of these streams are dammed by the Green River, thus forming backwaters. It appears that it is the backwaters that are preferred, rather than the actual streams. In many of the tributaries that squawfish do utilize, their upstream range is usually at the lower end of the trout, or cold water, zone. In the Green River of Wyomi ng, squawfi sh were reported to Green River, . Wyoming, but not above. In the Yampa River, only one has been taken above Craig, Colorado. In the Gunnison River, Delta, Colorado, appears to have been the upstream range of this species, although recently they have not been found this far upstream. Therefore, stream size, as well as summer temperatures, appear to be determining factors in habitat selection. The areas within a stream that squawfish use have been intensely studied in recent years. Young squawfish (1, 2, and 3 year old fish) prefer backwaters and other areas with slow current and usually a silt or silt-sand substrate (Figure 2) (Vanicek and Kramer 1969, Holden and Stalnaker 1975, Holden 1977, Twedt and Holden 1980). Changes in habitat selection during various seasons has not been noted. It is highly pro- bable that during winter, flowing portions of the river are utilized since many backwaters are frozen solid. Larvae in the Yampa and Upper Colorado rivers are found in a variety of calm habitats, often alongside rather swift currents. Since neither 6