The main objectives of the study reported were to gain fundamental knowledge of the dynamics of the populations of phytoplankton and of some of the principal environmental influences on the dynamics of these populations, and to determine primary production in a sewage oxidation pond. Preliminary measurements were made of short-term changes in phytoplankton concentrations at various depths in the pond and at different times of day. These short-term changes where then considered in designing a comprehensive phytoplankton sampling program to meet the overall objectives of the project. Along with samples collected to estimate the size of the populations of phytoplankton, simultaneous measurements were frequently made of solar radiation, the standing crop of Daphnia magna, ash-free dry weight of suspended matter, gross oxygen production, and community respiration. (Author)