Observers recorded visual scanning by four lifeguards at three indoor public swimming pools. Scanning increased as a positive function of the ratio of children to adult swimmers, i.e., scanning was greater when the ratio was high, suggesting that lifeguards became more concerned about the risks to children and the ability of nearby adult swimmers to monitor these children when the number of children significantly exceeded the number of adults. Absolute numbers of children, however, decreased number of scans, possibly because of greater number of incidents and rule violations requiring lifeguards' attention which competed with watching the pool. Lifeguards were more likely to scan a pool area when they were in elevated towers versus standing on the pool decks. Lifeguards' scanning declined later in the day, possibly due to fatigue or because of competing activities of pool maintenance.