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HABITAT REHABILITATION 231 Floodplain: not detailed I Upland Sediment Basin \ , Figure 4. Example of backwater isolation habitat rehabilitation and enhancement projects backwaters is a management goal. Figure 4 presents an example of a typical project; this project will isolate an Illinois River backwater and create three independently manageable compartments within it. Projects are typically designed to provide water level management capabilities to produce emergent and submersed aquatic plant communities. Few projects have been completed and none has been monitored following construction. Reduced fish access to backwater habitats may be detrimental to local fish populations (Bayley, 1991; Sparks, 1992; Shaeffer and Nickum, 1986a). Loss of river-backwater connections may also block energy transport from backwaters to the river (Schaeffer and Nickum, 1986b). Island projects Island projects (11 projects indicated by squares in Figure 1) include a variety of approaches, but the common goal is to reduce river flow or wave energy that transports or resuspends sediments. They are constructed to replace islands eroded by river currents and waves in the northern reaches of the Upper Mississippi River. In the southern reaches they are constructed to protect existing islands or to create islands in large open backwaters where they did not occur previously. Extensive monitoring on a single project in Wisconsin is in an early stage, but physical performance (creating a low turbidity environment downstream from the island) appears positive. CHANNEL MAINTENANCE STRUCTURES Channel maintenance operations are conducted to provide a minimum 2.7 m navigation channel during low flow periods. Navigation dams are used north of the confluence with the Missouri River, dikes are used south to the Ohio River) (Chen and Simons, 1986), are being modified to improve aquatic habitat conditions. Dikes (Neimi and Strauser, 1991). Areas between dikes and revetted banklines provide much of the low