Construction of large-scale, hydroelectric tidal power developments in the upper Bay of Fundy is receiving serious consideration. Potential designs involve ebb-generation with 1400- 5300-MW plants using 7.6 m diameter, straight-flow, low-head turbines installed in dams up to 8 km in length. Discharge through individual turbines will be 400 m3/second at 50 rev/minute with draft tube velocities of 11.4 m/second. Calculated parameters for these turbines are a water length of 2.26 m, impact velocity of 23.99 m/second, blade tip velocity up to 28.7 m/second and a total pressure flux of 1.7 atm. The existing environment is macrotidal (tide range 11-16 m). Embayments are homogeneous estuaries with extremely turbid water. The intertidal biological community is a salt marsh-mudflat biome. The pelagic zone supports large populations of migratory fishes, particularly the alosids, Alosa sapidissima, A. aestivalis, A. seudoharengus, and Clupea harengus. Striped bass, spiny dogfish, Atlantic salmon, and Atlantic sturgeon also constitute a significant portion of the fish community. Tagging experiments indicate this region is a northern migration terminus for American shad populations from all Atlantic coast rivers and abundance in an individual tidal basin is about 1.5 million adults during a single tidal cycle. Striped bass and alewife tagged in this region have been taken as far south as North Carolina. Upstream tidal headponds will have reduced tide ranges of 5-6 m and the lower energy will result in stratification of the water column and less turbidity. Increased sedimentation above and below the dams is expected to affect local soft-shell clam fisheries. Tidal barrages may alter fish migration routes and repeated passage through turbines during tide-related movements will cause significant mortality to both fish and marine mammals. Existing knowledge for fish passage design in this environment is inadequate for development of sound mitigation measures.