Water quality variables from three locations within the Chicago River sampled once per month from May through September 2023. Data provided by the Metropolitan Water Reclamation District of Greater Chicago. Chlorophyll-a measured in μg L⁻¹, Fecal Coliforms (FEC_COL; natural log transformed) as colonies per 100mL, temperature (TEMP) is in degrees Celsius, whereas all other variables are measured in mg L^–1. Other abbreviations include dissolved oxygen (DO), ammonia-nitrogen (NH3_N), nitrite and nitrate (NO2.NO3), total Kjeldahl nitrogen (TKN), and total phosphorus (Tot.P).