To predict possible effects of the dams and gates of the proposed Passamaquoddy Tidal Power Project on herring movement in and out of the Passamaquoddy Bay region, information was first needed on the swimming performance of the fish. Maximum and sustained swimming speed tests designed for this purpose indicated (1) that the maximum swimming speed for herring 60 to 219 millimeters long ranged from 2.3 to 4.4 feet per second, and (2) that the swimming endurance (length of time a fish was able to swim in a particular water velocity) for herring of similar lengths exposed to water velocities of 1.2 to 3.2 feet per second ranged from 1 to 115 minutes. If the fish responds in the field as in the laboratory, the filling gates that operate at flood tide and emptying gates that operate at ebb tide would not appear to prevent migration.