Mclean County, Illinois: drinking water report. McLean County in central Illinois has about 173,000 residents, with Bloomington-Normal as the population…
McLean County in central Illinois has about 173,000 residents, with Bloomington-Normal as the population center. The City of Bloomington draws from Lake Bloomington and Evergreen Lake, while Normal relies on groundwater. The county's agricultural economy – some of the most productive corn and soybean land in the world – drives the water quality challenges.
Lake Bloomington's watershed drains intensive row-crop agriculture, and the lake's nutrient loading reflects it. According to the Illinois EPA's 2024 lake monitoring report, total phosphorus in Lake Bloomington averaged 0.08 mg/L – well into the eutrophic range. The nutrient loading fuels algal growth and drives disinfection byproduct formation when the water is treated.
Atrazine in the lake peaks during spring planting season. A 2024 Illinois EPA compliance report noted that the Bloomington water system's running annual average for atrazine reached 2.1 ppb – below the MCL of 3 ppb but among the highest for municipal systems in Illinois. The Central Illinois Regional Airport has documented AFFF use, with PFOS at 6 ppt in nearby monitoring wells.
Bloomington's lake-sourced water faces the same agricultural pressure as most central Illinois surface water. The treatment plant manages regulated contaminants effectively, but disinfection byproducts from treating nutrient-rich water are worth monitoring at the household level.
Check your water for seasonal data. A carbon block filter reduces disinfection byproducts and atrazine effectively. For PFAS, add reverse osmosis. Our water filter guide covers systems suited to treated lake water. Pull your detailed report for seasonal trends, and visit our Illinois page for statewide data.