One of the more obvious ways in which a power plant can be expected to influence the environment is in its effects upon zooplankton entrained in the condenser cooling-water system. For example, Raymont (1964) and Raymont and Currie (1964) noted the consequences of such entrainment on the species composition of zooplankton. Much of the work on this subject has been reviewed by Naylor (1965) and Coutant (1970). The present report describes mechanical and thermal factors that may affect survival of zooplankton (apart from fish eggs and larvae) during passage through the cooling water condenser and heated water outfall of the Connecticut Yankee plant. Estimates are made of the proportion of the river zooplankton entrained by the plant.