This U.S. Geological Survey (USGS) Data Release provides high-resolution, nearshore, spatial water-quality data collected from Seneca Lake, New York, on July 9-10 and October 9-10, 2019. All data are reported as raw measured values and are not rounded to USGS significant figures. Continuous water-quality monitors were mounted to a boat at approximately 0.5-meters below the water surface and used to measure water nitrate, chlorophyll fluorescence (fChl), fluorescent dissolved organic matter (fDOM), dissolved oxygen, specific conductance, phycocyanin fluorescence (fPC), turbidity, pH, and temperature.