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19 backwaters might actually enhance exotic fish populations by providing a haven and increasing competition. Valdez and Wick (1981) suggested that backwater habitats created for endangered fish should function like natural backwater habitats to avoid becoming refugia for nonnative fishes. Backwaters formed at high flow should drain with descending flow and low flow backwaters should be inundated and flushed at high flows. Backwaters created from gravel pit ponds and connected to the river tended to be permanent and provided refugia for nonnative competitors by sheltering them from the riverine environment These should be sealed to prevent immigration of nonnatives into the river. Osmundson (1987) suggested that gravel-pit ponds be zoned away from the river or that very secure dikes be required to prevent sportfish from entering the river during high water events. Molles (1980) suggested the establishment of a semi-natural preserve for native fish fauna with natural flows and the exclusion of exotics. He suggested preservation of the entire community, not preservation of individual species. He admitted such an undertaking would be ambitious; but, once established it would require less management input than the continual stocking of hatchery populations. He admitted the major obstacle would be the elimination of exotics. Hubbard (1980) agreed, suggesting the "primeval-like" habitats found in the Yampa River within the upper basin made this river most suitable as a preserve. Hubbard (1980) believed that natives could probably cope with most nonnative fishes if provided with natural habitats. There appeared to be a need for standard protocols and review of stocking programs for nonnative fishes. Pimm (1987) suggested three rules for introductions to reduce severe impacts. Don't introduce species where predators (or competitors) are absent Don't introduce highly polyphagous species. Don't introduce species into relatively simple communities. Osmundson (1987) recommended that nonnative fish stocking by private citizens and public agencies into the river system should be discouraged If endangered fish are stocked in the upper basin they should be large enough to avoid predation. Osmundson (1987) recommended stocking fingerling Colorado squawfish into predator-free, grow-out ponds in the early spring and transferring them to the river in the fall. Size at release should be 200-250 mm TL to avoid most predators. Razorback sucker also should be stocked at a size (> 300 mm TL) relatively immune to predation (Marsh 1987; Marsh and Langhorst 1988; Marsh and Brooks 1989). Marsh and Langhorst (1988) pointed out that this might establish adult stocks but self-perpetuation would not occur if predation on larvae continued. Stocking in the late winter (January) helped razorback sucker acclimate to riverine conditions, find cover, and avoid predation (Marsh 1987). Marsh and Langhorst (1988) believed that recovery of razorback sucker "may best be achieved in backwaters, oxbows, and smaller tributary habitats amenable to substantial, perhaps repeated, removal of nonnative fishesll. They suggested a reduction of established populations of known predators through ichthyocides to remove catfish from selected, streams before stocking of razorback sucker.