Illness had been reported among person who had used a swim club pool. At least 53 illnesses were identified. The highest attack rates were observed among persons who visited the pool two days. No obvious source of contamination was identified. Interviews with swimmers and staff indicated that the water was visibly cloudy when the regular maintenance person was not on duty, and the pool usage was the highest. A kink in the tube that supplied chlorine to the pool was subsequently identified and repaired by the pool-maintenance manager. The pool was hyperchlorinated, and the pH was corrected to optimize chlorine efficacy. The pool was equipped with an automated chlorine feeder and filtration system and was monitored and maintained by lifeguards and a maintenance worker. Multiple lapses and inadequacies in pool management were identified. Of these, most remarkable were a lack of staff training and response policies and the absence of pool-chemistry monitoring or pool maintenance records.