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16 examined habitat data from fish collections on the Green River. They identified high spatial overlap in habitat use between young Colorado squawfish, red shiner, and fathead minnow and little overlap between squawfish and channel catfish. McAda and Kaeding (1989) also showed complete habitat overlap between YOY Colorado squawfish and red shiner, sand shiner, and fathead, minnow collected from the Green and Colorado rivers, Colorado and Utah. Habitat parameters analyzed were depth, velocity, and substrate averaged from each seine haul. Adult and juvenile Colorado squawfish were collected in association with both native and nonnative fishes in the White River. Introduced species associated with Colorado squawfish were common carp, channel catfish, fathead minnow, and red shiner. Colorado squawfish between 116-172 mm total length (TL) were collected with red shiner, fathead minnow, and common carp (Miller et al. 1982a). Adult Colorado squawfish apparently used the same habitats as northern pike, walleye, and channel catfish suggesting the potential for competitive interactions especially during periods of limited resource availability (Wick et al. 1985; Tyus and Karp 1989; Tyus and Beard 1990). Karp and Tyus (1990a) studied young Colorado squawfish interactions with six species (five introduced) of similar size in aquaria All nonnatives exhibited relatively high amounts of interspecific aggression, including green sunfish, black bullhead, fathead minnow, redside shiner, and red shiner. Green sunfish, fathead minnow, or red shiner were frequently observed chasing smaller Colorado squawfish. Territorial behavior was observed only for green sunfish and fathead minnow. Fathead aggression was attributed to breeding behavior. They observed one incident of aggression resulting in physical injury with a fathead minnow nipping a small Colorado squawfish. Colorado squawfish may be competitively inferior in a crowded or resource-limited environment based on its non-aggressive nature and slower pursuit of prey items. Habitat alterations by introduced fish Habitat can be altered by consumption, uprooting, or increased turbidity as a result of nonnative fish activities. Water quality can be degraded by siltation, substrate erosion, or eutrophication. Some species may cause habitat degradation by uprooting vegetation or consuming large numbers of aquatic plants. These feeding strategies may be novel to the biotic system and increase turbidity and siltation or cause degradation of water quality. No incidents of habitat alteration by exotics in the upper basin have been reported Common carp have been implicated in the removal of aquatic vegetation in other systems but their affect on vegetation in the upper basin is unknown. Moyle (1976) reported carp decreasing the clarity of a lake in California due to uprooting vegetation. Hybridization Hybridization with native species can occur between closely related species. This usually occurs through interbasin transfer of a nonnative from an adjacent basin. One