Water management of the Lewis and Clark Lake for flood control, hydroelectric power, navigation, and other purposes affected fish population levels. Fluctuating water levels in May and June affected fish spawning and survival of young. Suggested management measures may improve sport fish abundance, such as construction of spawning and nursery ponds near the reservoir or maintenance of higher water levels during May and June to enhance the reproduction opportunities for desirable species are either too costly or inconsistent with the primary flood-control function of the reservoir. Fish abundance with the present water management regimen will probably remain similar to that of the early 1970's.