A chemical and biological study is described for Mumford and Palmer Coves near Groton, Connecticut. Mumford cove is an estuary receiving 0.25 MGD of primary-treated sewage effluent prior to construction of a secondary treatment plant with projected flow of 6 MGD. Palmer Cove, an adjacent, unpolluted cove, was used as control. Analyses included temperature, salinity, dissolved oxygen, BOD, nitrate, and phosphate. Counts were made of total bacteria, total and fecal coliforms, fecal streptococci, phytoplankton, and benthic invertebrates. Results indicated that nitrate, phosphate, and dissolved oxygen levels at the current outfall area at the head of the receiving cove are occasionally high enough to suggest that the increased flow of fresh water and nutrients into the saline cove may produce adverse effects in terms of stimulating the growth of existing populations of flagellated phytoplankton. The control of the problem by extending the outfall areas is discussed.