The lengths of creek chubs, Semotilus a. atromaculatus, of the same year class differ significantly in the various pollutional zones of Lytle Creek, Clinton County, Ohio. In the clean-water zone above a sewage treatment plant outfall, where the stream is very small, the 0-year creek chub taken in August 1952 averaged 42.3 millimeters in total length. The creek chubs of the same year class, found in the upper portion of the recovery zone, averaged 53.3 millimeters, while in the enriched lower portion of the recovery zone they were larger, averaging 63.8 millimeters. In the lower clean-water zone, the fish were smaller and had a mean length of 52.0 millimeters.