The Rathbun Fish Hatchery utilizes 20 outdoor circulating ponds for fish rearing purposes. These ponds are semicircular with a center drain and were designed to be "self-cleaning". At water flows typically used for fish production, however, excess feed and fish waste accumulated in stagnant areas on the pond bottom causing unsanitary conditions. That's really a politically correct way of saying they stink and support disease. A method was needed to increase pond velocity without increasing water flow and without compromising fish health. Dr. Donald F. Young, Dr. Bruce Munson, and Bill Stein of Iowa State University Department of Aerospace Engineering and Engineering Mechanics were consulted to address this problem. Drs. Young and Munson and Mr. Stein developed a scale model of the pond in which they could test solutions to this problem. Model tests indicated a flow of 700 gallon per minute or a flow rate of 500 gallon per minute in combination with a drawdown to half depth would clean the pond. Such flow rates, however, would not be practical from a fish rearing or water use standpoint. A baffle system was tested but rejected. Final recommendation was use of a submersible pump capable of pumping 285 gallon per minute. The pump is placed on the bottom once the pump outlet located midway between the drain the outer pond wall. The resulting increase in water velocity effectively flushes settleable solids from the pond. Use of the pump to flush the pond eliminates the need to physically clean the pond during peak production months when fish are most stressed and prone to disease outbreaks.