Several water filters constructed of Saran cloth of different porosities were tested for efficiency in filtering undesirable firsh from hatchery pond water supplies. A cloth filter bag, attached to pond water supply pipes, gave promising results. Thirteen ponds tested with these filters were free of wild fish (fish not stocked in test ponds by hatchery personnel) af,ter periods ranging from four to 29 weeks. The remaining four test ponds contained a total of 16 wild fish. Control ponds were heavily infested with wild fish species introduced through the water supply.