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4. Within four months following draining, removal of nonnative fishes, and construction of a connection channel, nonnative fishes invaded and recolonized Gardner Pond. Within eight months, five species of nonnative fishes had successfully reproduced in Gardner Pond. Two conclusions were evident: a) Gardner Pond had again become a haven for nonnative fishes, and b) nonnative fishes are extremely resilient. Any ponds, whether in the 10-, 50-, or 100-year floodplain with bottoms irregularly shaped and contoured as depressions, provide perennial, off-channel habitats for nonnative fishes to grow and reproduce. Such ponds that are connected to the river allow sub-adult and adult nonnative fishes uninhibited access to the river and to other off-channel habitats connected to the river. Although such ponds are used by native fishes only during runoff, nonnative fishes appear to benefit more from such perennial, lentic habitats. In any event, ponds with depressions provide a constant supply source of nonnative fish that can potentially escape to the mainstem river. 5. Hotspot Pond did not drain following runoff in 1996. Therefore, an accurate assessment of whether nonnative fish populations could be reduced or eliminated was not possible. Usually, during low-water years, this pond is almost entirely dewatered by late-August or early- September leaving only a mud flat at the upper end. Irrigation waste water that flows through the pond to the river is the only source of water. The only habitat available for fish is..near the connection channel near the river. However, during high-water years, such as 1996, this pond does not completely drain leaving adequate water depths for fish to survive during the winter. In addition, groundwater levels during high-water years probably help retain pond water levels longer than during low-water years. 6. If ponds are reclaimed, steeper bottom slopes than that found in Hotspot Pond will be required for ponds to drain during high-flow years to reduce or eliminate perennial habitat for nonnative fishes. ECOLOGICAL FUNCTIONS OF A RIVERINE SYSTEM Welcomme (1985) and Ward and Stanford (1995) emphasized that the diversity, resilience, and integrity of large river ecosystems are related to the connectivity of the main channel and its associated floodplain. However, there is an increasing trend in regulating streamflows of large river systems to increase the productivity of basins for agriculture and increase safety for human occupation. Such modification of the aquatic environment generally adversely affects the fish stocks in large river systems (Welcomme 1985). Welcomme stated that the majority of riverine fishes have been extremely sensitive to modifications in the flood cycle and other environmental alterations caused by human activities to regulate streamflows. He also pointed out that substantial shifts in the composition of the fish community and the introduction of nonnative species result in uncertainty of restoring fish assemblages by simple natural processes. Welcomme emphasized that planning in river management must include the floodplain since these areas are essential to maintain fisheries. 21