This data release includes vertical water-quality profile data collected from April 2022 to April 2024 at three locations in the Saugatuck River Embayment near Saugatuck, Connecticut, and two locations in the Mill River and one at the mouth of Sasco Brook near Southport Harbor, Connecticut, for the Sasco-Southport Embayment that discharge to Long Island Sound. These data were collected by the U.S. Geological Survey, in cooperation with the Connecticut Department of Energy and Environmental Protection and the U.S. Environmental Protection Agency, to support the management of nutrients in Connecticut discharging to Long Island Sound. The vertical water quality data were collected using multiparameter water-quality sondes and photosynthetic active radiation (PAR) sensors. The observations measured include water temperature, specific conductance, salinity, dissolved oxygen, pH, turbidity, chlorophyll a, water depth, PAR in water, and PAR in air, air temperature, and barometric pressure.