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Chronic escapement of nonnative fish species into the rivers would continue through outl ets from the ponds or when high streamflows cause overbank flooding.' The negative impacts on the endangered Colorado River fishes from predation and competition by nonnative, warmwater fishes would continue. This situation is not conducive to the Recovery Program goals and objectives to recover the endangered fishes in the Upper Colorado and Gunnison rivers. B. Alternative 2 - Mechanical or Chemical Control of Nonnative Fish Species From Ponds in the FloodDlain. 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. Mechanical or chemical control of nonnative fishes could occur in a maximum of 25 ponds in 1997 and up to 150 ponds through the Year 2002 (Martinez and Nesler 1996). In reality, mechanical or chemical control techniques would be employed in about 10 ponds during 1997. Criteria for Selectinq Ponds. Ponds will be identified as to location in the floodplain (i.e., some in 10-year and 50-year floodplains). Access for controll i ngnonnat i ve fi shes woul d be acqui red from 1 andowners who are willing to cooperate. One objective of the proposed control measures is to determine if nonnative fish control in floodplain ponds within a given river reach contribute significantly to reductions in the abundance of nonnative fishes in riverine nursery habitats that include backwaters, embayments, and floodplain habitats that connect with the river. Therefore, the initial proposed control measures are considered experimental and will be carefully evaluated. DescriDtion of Mechanical or Chemical Control. Ponds may be drained mechanically using large-volume pumps. The fish could then be seined or trapped for removal if feasible. If the ponds were pumped to the point that dissolved oxygen became low, the nonnative fishes would die from suffocation. Water freely percolates through the gravel in some ponds where complete draining would be impossible. In these ponds, the remaining water treated with rotenone to kill nonnative fishes. Other ponds may be treated with rotenone without draining if water recharge occurs quickly or if it would be logistically impractical to get the large pumps .to the site. All chemical treatments will be made using the Colorado Division of Wildlife Chemical Application Operating Procedure as standard protocol. Rotenone would be applied at a concentration of 3 milligrams per liter, mg/l (parts per million, ppm) following the label directions with this registered piscicide. Fish absorb the chemical through the gills and are killed by the interruption of respiration within the body cells (Lindahl and Oberg 1961). Each crew woul d be supervi sed by a person who has been cert i fi ed by the State of Colorado to apply chemicals. Rotenone has been found to be safe to humans when applied by certified applicators following label instructions (Sousa et al. 1987). Rotenone is extremely toxi c to many spec; es of invertebrates arid fi sh (Bradbury 1986). However, the toxicity of rotenone varies among various 15