Lake Lemon was constructed during 1953 in a hilly (average relief of about 100 feet), heavily wooded drainage basin. Considerable lakeside development has taken place after impoundment, and as a result concern has arisen about the sedimentation rate in the lake. This study was undertaken to determine the sedimentologic conditions and the total sediment accumulation in the lake and to relate these determinations to the geology of the drainage basin. Lake Lemon is on the boundary between Monroe and Brown Counties about 9 miles northeast of Bloomington. The lake is used presently for flood control, low-flow augmentation, and recreation. It was used for water supply and is being considered as a future auxiliary and emergency supply for Bloomington. The reservoir has a surface area of 1,440 acres at the spillway (crest) elevation of 630 feet above sea level. The original lake volume at that level, as computed by the U.S. Geological Survey and verified by this study, was 14,400 acre-feet. Because of the siltation during the past 20 years, the present lake volume corresponding to the 630-foot pool is 13,920 acre-feet, which represents an approximate 3 ½-percent decrease in reservoir volume.