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Although native Americans along the Colorado River constructed canals and reservoirs for agriculture (Powell 1961), irrigated agriculture did not become extensive until the 1920's (Hunt and Huser 1988). Broad river valleys in the Upper Basin were colonized by people who began to construct levees for flood control (Fradkin 1983). As dams were constructed in the Upper Colorado River Basin, the historic peak spring streamflows decreased thereby allowing people to construct levees that more easily controlled overbank flooding. Marshes and floodplain habitats disappeared as levees were built to "control" the river from regul arly fl oodi ng agri cultural 1 ands. These changes have severely reduced connectivity of the river system to floodplain habitats. Streamflow regulation through the operation of Flaming Gorge Darn decreased the frequency of overbank flows. At the same time, levees were constructed in the extensive floodplain reach of the middle Green River by private landowners who realized that they could contain the river channel for agriculture. Levees were also constructed on public lands in the Green River on properties (Brown's Park National Wildlife Refuge and the Ouray National Wildlife Refuge) acquired to mitigate for losses in waterfowl habitat from construction of the darn. The endangered Colorado River fishes (razorback sucker, Colorado squawfish, Ptvchocheilus lucius, and perhaps bony tail , Gila eleQans) historically utilized low velocity habitats that occurred in unrestricted meander or braided reaches and floodplain habitats associated with broad valleys in the Upper Basin. This report summarizes the published literature about the ecological importance of floodplains to riverine fish communities and relates this literature to reports that have been developed through the Recovery Program for endangered fishes in Upper Colorado River Basin (Wydoski and Hamill 1991). It also emphasizes the need for concurrent integration of three Recovery Program elements: habitat enhancement/restoration, control of nonnative fishes, and captive propagation. III. ECOLOGICAL FUNCTIONS OF A RIVERINE SYSTEM Welcomme (1995) 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 safer 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 cause 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 that by simple natural processes. Welcomme emphasized that planning in river management must include the floodplain since these areas are essential to maintain fisheries. The importance of the land-water interface to the productivity of lotic systems has been recognized for over twenty-five years (Allan 1995; Hynes 1970; Hynes 1983). However, interpretation of the complexity of biological responses and importance of geomorphological or hydrological processes has occurred only 3