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0Q:0576 fishes (i .e., food is shared) in the Upper Colorado River (Jacobi and Jacobi 1982; Grabowski. and Hiebert 1989). Nonnative fishes have expanded rapidly in the Upper Basin between 1986 and 1992 as indicated from the Interagency Standardized Monitoring Program where they constitute 96.7 to 99.6% of the total numbers of fish collected from backwaters by seining (McAda et ale 1994a,b; 1995). Native and nonnative fish share the same backwater habitats. Although direct compet it i on among endangered' fi shes by nonnative fi shes has not been documented, limited food resources, sharing of the food resources, and use of the same habitats with low water velocity supports the belief that competition has also contributed to the decline of some native Colorado River fishes. II. ALTERNATIVES CONSIDERED , Five alternatives were considered in this Environmental Assessment regarding the control of nonnative, warmwater fish species in floodplain ponds along the Colorado and Gunnison rivers. Alternatives 2, 3, and 4 offer several methods that offer control of chronic escapement of the nonnative fishes. A. Alternative 1 - No Action. Under this alternative, nonnative, warmwater fish species in floodplain ponds along the Colorado and Gunnison rivers would continue to enter the river through outlets or during high streamflows that connect the ponds with the rivers. B. Alternative 2 - Mechanical or Chemical Control of Nonnative Fish Species From Ponds in the Floodplain. Under this alternative, mechanical (i .e., draining ponds, netting, electrofishing, etc.) or chemical (i.e., use of registered piscicides) control methods would be used to remove nonnative fish species from floodplain ponds along the Colorado and Gunnison rivers. C. Alternative 3 - Install Mechanical Devices in Outlets of Ponds in the Floodplain to Prevent Chronic Escapement of Nonnative Fish Species. Under this alternative, mechanical devices (i .e., screens or traps) would be installed in floodplain ponds with an outlet to either the Colorado River or Gunnison River. D. Alternative 4 - Slope the Bottom of Ponds in the Floodplain and Reconnect the Ponds with the Rivers. Under this alternative, floodplain ponds would be reconnected to either the Colorado River or the Gunnison River if the bottoms could be sloped so that they drain into the river as the streamflows subside. E. Alternative 5 - Fill Gravel-Pit Ponds Upon Completion of Gravel Mining Operations. Under this alternative, gravel-pit ponds in the floodplain of the Colorado and Gunnison rivers would be filled upon completion of new gravel mining operations. 7