This data release includes vertical water-quality-profile data from April 2021 to April 2023 at four stations in the Mystic River embayment and three stations in the Norwalk River embayment in Connecticut. These stations are part of a discrete and continuous water-quality monitoring project in embayments on Long Island Sound to support nutrient management activities in Connecticut. The 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 Long Island Sound Study. The data were collected using multiparameter water-quality sondes and photosynthetic active radiation (PAR) sensors. The parameters collected were water temperature, specific conductance, dissolved oxygen, pH, turbidity, chlorophyll, water depth, PAR in water, and PAR in air. Vertical water quality profiles are collected in conjunction with discrete water quality sampling ideally within the identified channel of the embayment during various tidal cycles. Data collection began in April 2021 and occurred twice a month from May 2021 to October 2021, and then monthly from November 2021 to April 2023.