The decision to remove an existing fish community with rotenone, a fish toxicant, is made only when few sport fish are present and their salvage is not cost effective. The cost of renovation is much lower when the water volume is reduced through reservoir drawdown. When refilled, the reservoir will be stocked with desirable sport fish. Irregularities in a reservoir's basin attract and concentrate fish. Deep reservoirs also are less subject to fish kills than shallow ones.
Shoreline erosion caused by wave action gradually enlarges reservoirs.
However, the extra water created is shallow, it absorbs the power of crashing waves and supports few fish. By removing silt from areas close to shore and depositing it at the existing bank, deep, fish supporting water can be created within casting distance of the bank. Sediment spoil excavated from the basin also can be relocated in the basin as islands. Islands must be stabilized with rock riprap to prevent erosion. Trapping sediment above the reservoir where it can be removed periodically keeps the water in the reservoir clearer than if sediment is allowed to accumulate in the basin or remain suspended.