Lakes are important resources and understanding relationships between fish, humans, and environmental conditions is critical for guiding management activities. We examined fish populations, limnological conditions, lake basin morphology, and watershed characteristics in 129 Iowa lakes. Our purpose was to evaluate patterns in population characteristics of important fish species in relation to environmental conditions. Bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides abundance was highest in systems with high water transparency and nutrients. Catch rates of bluegill, black crappie, and largemouth bass were generally low when omnivores (e.g., black bullhead Ameiurus melas, common carp Cyprinus carpio) were present. Body condition of the study species was highest in highly productive lakes with clear water. Bluegill and largemouth bass condition and bluegill growth showed evidence of density dependence. This study suggests that high water transparency generally resulted in high relative abundance, good condition, and fast growth of sport fishes in Iowa's highly productive lakes.