Historical accounts of Onondaga Lake dating to the 1600's indicate that the lake once supported a coldwater fishery. By the late 1800's, severe degradation of the lake and adjacent tributary environments was accompanied by declines in the American eel (Anguilla rostrata), and extirpation of Atlantic salmon (Salmo salar) and whitefish (Coregonussp.). Nine faunal surveys were conducted from 1927 to 1994. We used rarefaction analyses to standardize survey results by computing expected species richness values (E(Sm)) relative to the 1946 gill net catch (7 species, m=164 individuals). Linear regression applied to the expected richness values (E (S164)) over time showed a significant increase in richness from 1946 (YEAR=0) to 1994 (YEAR=47) for fish caught in gill nets [E(S164) = 0.153*YEAR + 6.785, r2=0.79, P<0.005] and trap nets [E(S164) = 0.226*YEAR + 3.723, r2=0.89, P<0.01]. Although species richness has increased, almost half of the species captured since 1989 show no evidence of juvenile recruitment from within the lake. This result points to the role of immigration in maintaining lakewide diversity. The present community structure has developed from 1) species specific declines and extirpations, 2) invasion and establishment of pollution tolerant species, and 3) fishes interacting with refugia.