A sonar fish counter installed at the Pinopolis Dam navigation lock near Moncks Corner, South Carolina in 1975 was used during the last 3 springs to enumerate blueback herring (Alosa aestivalis Mitchill) passing into the Santee-Cooper Lakes. Construction of the biomass fish counter was based on the design of salmon smolt counters used successfully in Alaska. Characteristics of fish movement and schooling patterns were determined and their relationship to accurate counting of herring was evaluated. Initial tests to prove the accuracy of counts were not successful. However, other population indices indicated that trends were accurately assessed.