Depth distribution of the bluegill, Lepomis macrochirus Rafinesque, in farm ponds was determined by the use of fish traps. Results indicated that during summer stratification bluegills were found in greatest numbers in shallow waters. They were unable to live for extended periods of 6 to 45 hours at water depths where the dissolved-oxygen concentration was 0.3 p.p.m. or less accompanied by a carbon-dioxide concentration of 4.4 p.p.m. or more. This condition was therefore considered to be the critical combined dissolved-oxygen and carbon-dioxide concentrations for bluegills and the depth that these concentrations usually occurred was designated as the critical depth.