High frequency water-quality measurements were collected by the U.S. Geological Survey within Willow Creek Reservoir located in Heppner, Oregon. All measurements were taken at 0.5 meters below the surface with a YSI EXO2 multiparameter sonde. Information collected include location, time, water temperature, pH, specific conductance, dissolved oxygen, total chlorophyll, blue-green algae phycocyanin, and turbidity. The measurements were collected while boating around the reservoir at about 4 kilometers per hour. These data were collected on June 9, 2015, August 17, 2016, and September 16, 2016, and are published as individual datasets for each date.