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' Spring flow is the most important annual event that shapes the channel, and thus, the habitat of the Gunnison River. High spring flows create and maintain ' the braided channels that provide a variety of important habitats for endangered and other native fis hes. High spring flows inundate the floodplain, providing annual nutrients via sediment deposition in the riparian corridor. Reduced flood ' frequency has had several repercussions to instream habitats as well as to floodplain dynamics. Instream physical changes include, 1) gradual simplification of the river channel--side channels and backwaters are lost through silt deposition and are not available to native fishes, 2) sand bars are ' invaded by tamarisk which stabilizes them and makes them resistant to shifting, and 3) gravel-cobble substrates become armored or imbedded with silt which reduces their utility as spawning substrate for fish and habitat for a variety ' of macroinvertebrates. Changes to the floodplain include, 1) fewer backwaters and oxbows being created and maintained, 2) reduced areas suitable for cottonwood regeneration, 3) reduced frequency of a connection of the river with existing ' backwaters and oxbows, 4) reduced or complete loss of flushing of the floodplain soils to remove salts (Cooper and Severn 1994c), and 5) reduced or eliminated access to areas vital to survival of endangered fishes. ' Irrigation Practices at Escalante SWA. The Hamilton Tract has-water rights from both the Don Quixote and Hartland Ditches. A surface irrigation return that delivers administrative spill from the Hartland Ditch to the Gunnison River is located on the eastern boundary of Site 1 at the Escalante SWA. Irrigation water used for private agricultural purposes to the north of the Hamilton Tract returns via diffuse subsurface routes through the tract. Fish and Wildlife Resources ' During 1992 and 1993, the warmwater stream reaches of the Gunnison River from the North Fork of the Gunnison River to the confluence with the Colorado River near Grand Junction were intensively inventoried by the USFWS. Eighteen fish species and three catostomid hybrids were captured during this sampling. In the immediate area of the Escalante SWA, three native fish species, flannelmouth sucker (Catostomus Iatipinnis), bluehead sucker (Catostomus discobolus), and roundtail chub (Gila robusta) comprised about 80% of all fish encountered in the reach. Other non-native fishes that were frequently collected included carp (Cyprinus carpio), fathead minnow (Pimephales promelas), red shiner (Cyprinella lutrensis), and white sucker (Catostomus commersoni). Other non- native fish that were occasionally captured in off-channel, low-velocity habitats included green sunfish (Lepomis cyanellus), black bullhead (Ameiurus melas), and northern pike (Esox lucius). These three non-native game fishes that thrive in ' low-velocity habitats in the Gunnison River could hamper endangered fish recovery efforts because they may potentially prey upon young razorback sucker and other native fishes. Presently, there are two small impounded areas within Site 1 that could become connected to the river via the spillway at the downstream outlet during high spring flows. However, it is unlikely that any fish species could survive ' for extended periods because these two areas are too shallow and probably lack sufficient dissolved oxygen. These two depressions probably remain wetted by irrigation returns from private agricultural fields to the north. It is possible 1 9