The Coralville Reservoir is a flood control impoundment located on the Iowa River just upstream from Iowa City. Since being placed in operation in 1958 its capacity at conservation pool level has been reduced nearly 20% by sedimentation. Studies of the reservoir\u27s fishery have been conducted since 1961. Fish population surveys do not indicate a noticeable modification of the fish population due to siltation. A decrease in the total fish population, primarily sport fish, occurring early in 1965, was due to oxygen depletion caused by heavy farm land runoff. Limnological studies of the Iowa River and the reservoir have been in progress since 1964. These indicate that gradual increases in plankton populations and threshold odor values have occurred in the reservoir and the river below the impoundment. Studies of the biological productivity of the reservoir indicate that maximum production frequently accompanies increased water level and inundation of littoral areas. Thus, increasing reservoir conservation pool level to compensate for loss of capacity due to sedimentation could contribute to water quality problems due to eutrophication
