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258 Flooding and Aquatic Ecosystems be sufficient to maintain self-sustaining populations after the stocks have become reestablished and adequate spawning, nursery, feeding, and rest- ing habitats are available to them. Actions Required to Increase Survival of Razorback Sucker Larvae Various actions involving streamflow management, habitat development and maintenance. management of nonnative fishes, and captive propa- gation/stocking must be integrated and performed concurrently if self- sustaining populations (Le., recovery) of razorback suckers are to be realized. Streamflows necessary to provide an adequate frequency of in- undation of floodplain habitats must be provided as often as possible to increase survival of razorback sucker larvae during their critical period. Ex- isting floodplain terraces were deposited and maintained by peak spring streamflows that occurred before high dams regulated the flows. Even if existing levees are removed, present managed streamflows in the Upper Basin will not permit inundation of floodplain terraces long enough for razorback sucker larvae to grow sufficiently large to escape predation by nonnative fishes. It may be necessary to excavate existing terraces to allow the rivers to inundate floodplains. If increasing the frequency and duration of flooding through breeching levees, excavating terraces, and increasing streamflows is not possible, then floodplain depressions with abundant aquatic vegetative cover may provide habitat that will prevent extinction of the razorback sucker. Based on the published literature, it is not practi- cal to attempt to control nonnative fishes on a large-scale basis (Wiley and Wydoski, 1994) in Upper Basin rivers. Therefore, nonnative fish manage- ment should be emphasized in river reaches that are immediately upstream or downstream of floodplain habitats that are already connected or are re- connected to the rivers. The razorback sucker is nearly extirpated from the upper Colorado River, and captive propagation and stocking will be required to reestablish this species by using genetics conservation guide- lines (Williamson and Wydoski, 1994). Balance of Preservation and Use of River-Floodplain Environments Water is one of the 'most precious natural resources on Earth, particu- larly in arid and semiarid regions. This is reflected in human habitation of river floodplains on all continents. For example, most of the popula- tion (65%) in China inhabit river floodplains that constitute about 10% of China's landscape (Dudgeon, 1995). Another example is Bangladesh where 125 million people inhabit 70,000 km2 of floodplain in the deltas of the Ganges and Brahmaputra Rivers (Wohl. Chapter 1, this volume). In northern temperate regions, river-floodplain ecosystems have been altered so that longitudinal (headwater-river-estuary), lateral (river-floodpIain- riparian zone), vertical (surface water-groundwater), and temporal (time scale) dynamic and complex interactive pathways are disrupted (Ward and Stanford, 1989). Humans will continue to dominate water use of river ecosystems and in the process dramatically reduce the environmental integrity, productivity, biodiversity, and heterogeneity of these ecosystems (FrisseIl et aI., 1993).