DeKalb County Water Report

DeKalb County earns a B grade for drinking water quality, scoring 66.0 out of 100. Over the past five years, EPA SDWIS records 3 health-based violations — a small cluster that warrants attention.

Under the Clean Water Act §303(d), EPA ATTAINS tracks whether waterways meet quality standards for drinking, recreation, and aquatic life (reporting cycle: 2022). A substantial 38.6% of assessed waterways are impaired (96 of 249 water bodies) across DeKalb County's watersheds. The leading impairment causes are mercury and polychlorinated biphenyls (pcbs). Impairment does not mean tap water is unsafe — it measures ambient waterway conditions upstream of treatment, not finished drinking water.

USGS NWIS gauge data (as of 2026-05-14T12:45:00.000-06:00) puts SOUTH BRANCH KISHWAUKEE RIVER at 173.0 cfs — well below its long-term average at 57% of mean — low-flow conditions worth noting for water-dependent ecosystems. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. DeKalb County has moderate coverage with 15 active monitoring sites with 2,907 recent measurements on record. Predominant monitoring categories include physical and inorganics, minor, metals. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.