Hydraulic investigations were conducted on three types of fish-rearing ponds: The Foster-Lucas, circular, and raceway. Models constructed on 1/10 scale effectively reproduced the hydraulic conditions found in the prototypes. Flow patterns were observed by means of floats and dyes. The degree of short circuiting, mixing, apparent detention time, and probably flowing-through time were determined by means of dye injection in the water inflow and measurements of the time of appearance and concentration of the dye at the outflow. Differences between the hydraulic characteristics of the three types of ponds were closely correlated with known differences in their physical and biological characteristics. The four major criteria used to establish pond efficiency were carrying capacity, disease inhibition, food distribution, and facility of cleaning. Of the ponds studied, no one type could be considered superior under all conditions of fish-cultural operations. The Foster-Lucas pond, however, was definitely inferior to either the circular or raceway type.