Effects of a plunging water flow on the behavior of green sunfish (Lepomis cyanellus) 7.1 to 9.7 cm in total length were studied at the outflow of a 1.6-ha pond. Jumping ability and behavior were measured at 12-hr intervals using a fish's position in a 0.9 m2-vertical grid or in the discharge pipe. Activity was influenced by flow rate, time of day, and time of year. Fish jumped up to 10 times their body length and traversed a horizontal distance of 0.6 m. Fish with the greatest mean length jumped the highest. The majority of the fish were captured during the 0600-hr tending period: 79.9% pipe only study and 82.4% pipe and grid combined study.