Fond Du Lac County, Wisconsin: drinking water report. Fond du Lac County sits at the south end of Lake Winnebago in east-central Wisconsin, with about…
Fond du Lac County sits at the south end of Lake Winnebago in east-central Wisconsin, with about 103,000 residents. The City of Fond du Lac draws from Lake Winnebago, while surrounding communities rely on groundwater from the Silurian dolomite and deeper sandstone aquifers. Dairy farming dominates the rural landscape, and the county's geological transition from shallow dolomite bedrock to deeper sand and gravel creates sharply different water quality conditions depending on location.
The western and southern portions of Fond du Lac County, where thin soil overlies fractured dolomite, show the highest groundwater contamination rates. According to the Wisconsin DNR's 2024 monitoring data, 21% of private wells tested in these areas exceeded the nitrate MCL. The fractured rock provides preferential pathways for manure and fertilizer to reach the aquifer, bypassing the natural filtration that thicker soil provides.
Fond du Lac's Lake Winnebago supply faces algal bloom challenges similar to other lake-sourced systems. A 2024 DNR lake monitoring report found microcystin at 2.4 ug/L in Lake Winnebago during the August bloom peak – requiring enhanced treatment at the water plant to meet the 1.0 ug/L drinking water standard.
Your risk in Fond du Lac County depends on whether you are on the lake water system or a private well. Lake water is treated for algal toxins, while well owners over fractured dolomite face elevated nitrate risk with no treatment unless they install it themselves.
Check your water for data at your location. For well owners, reverse osmosis is the most effective nitrate treatment. For lake water users, a carbon filter handles algal taste compounds and disinfection byproducts. Our water filter guide covers both. Pull your detailed report for seasonal trends, and visit our Wisconsin page for statewide data.