This data release contains water quality data from discrete sonde profiles taken at 10 sites on Lake Koocanusa from 2019 through 2024. The profiles include measurements of water temperature, specific conductance, dissolved oxygen, pH, turbidity, and chlorophyll relative fluorescence as well as the depth of the sonde below the water surface. These data were collected as part of a water-quality monitoring program in Lake Koocanusa to provide data for Federal, State, Provincial, and Tribal entities in the United States and Canada.