A study was made to determine the effects of pressures likely to be encountered in a pumping station in Maine. Experiments were conducted with chain pickerel, yellow perch, fall fish, common shiner, lake trout and Atlantic salmon. Test fish exhibited extreme and erratic violent swimming activity for the first few seconds after exposure to a pressure of 300 psi. Salmon, lake trout and fall fish experienced no mortality during the 7-day period after exposure. Sixty percent of yellow perch died after 7 days.