AbstractThe standing crop and primary productivity of a small eutrophic, prairie‐parkland lake were measured. In general, both standing crops and primary productivity were large, 29.4 and 73.09 mg chlorophyllam−3and m−2and 78.71 and 196.77 mg C hr−1m−3and m−2respectively. Productivity decreased with increasing depth, therefore, decreasing light intensity. Relations between productivity and chlorophyll a content, productivity and light intensity, phytoplankton productivity efficiency and light intensity, productivity and water temperature were investigated, as was the photosynthetic index. Experiments designed to determine the photosynthetic capacity of the phytoplankton distinguished between actively growing and senescent populations. The latter were present during the winte