This dataset includes high-frequency sensor data collected during four consecutive summers from buoys deployed at main channel and backwater sites in Pool 8 of the Upper Mississippi River from 2015-2018. It also includes the event-specific concentration-discharge metrics (hysteresis and slope) calculated by combining the water quality sensor data with discharge data from a nearby USGS gage in Winona, MN (05378500). High-frequency sensor data were collected using water quality buoys (PISCES monitoring platforms; EMM350 Water Monitoring Pontoon Platform | ysi.com | ysi.com; Yellow Springs, Ohio) set up with EXO2 Multiparameter Sondes (YSI, Inc, Yellow Springs, Ohio) to monitor hourly or bi-hourly concentrations of chlorophyll-a, phycocyanin (metric of cyanobacteria abundance),, fluorescent dissolved organic matter (FDOM; QSU), and turbidity (FNU), and water temperature (Celsius) as well as a SUNA v2 nitrate sensor (Sea-Bird Scientific, Bellevue, Washington) to monitor nitrate concentration.