Road salt in our lakes, waterways, and drinking water

Lakes & Waterways

Our local lakes, waterways, groundwater, and soil have been absorbing virtually all of the salt spread in the city for more than six decades. Chloride from salt is toxic to small aquatic life and degrades the natural eco-system of our lakes. Once salt is in our waterways, it does not break down.

Environmental groups like the Friends of Lake Wingra, Friends of the Yahara River, and Friends of Starkweather Creek have joined the WI Salt Wise partnership, an initiative focused on raising awareness about responsible salt use.

Lake Wingra

Average chloride concentrations in Lake Wingra have been increasing by about 2 milligrams per liter (mg/L) per year since 1962. In 2016, the average chloride level in Lake Wingra was more than 100 mg/L, about ten times what it was in the early 1960s.

Lakes Mendota, Monona, Kegonsa and Waubesa

Our larger lakes are not immune from the impact of salt. Chloride levels in Lakes Mendota, Monona, Kegonsa and Waubesa have been increasing by about 1 mg/L per year since 1962. In 2016, Monona, Kegonsa and Waubesa all had chloride levels averaging more than 60-70 mg/L. Chloride levels in Lake Mendota averaged around 50 mg/L.

Smaller water bodies

Chloride levels exceeding the Chronic Toxicity Criteria for small aquatic life have been observed in Dunn’s Marsh, University Bay Creek, and Starkweather Creek. Local creeks and marshes are strongly affected by seasonal spikes in chloride. Some shallow groundwater has become a chloride sink, slowly releasing elevated chloride to surface waters.

Chloride concentration data

Download chloride data for our lakes, collected by Public Health Madison & Dane County.

Drinking Water

Madison’s drinking water source is groundwater. Road salt is beginning to contaminate parts of our groundwater aquifer.

Salt is made up of two chemicals, sodium and chloride — chloride is responsible for the “salty” taste. Water begins tasting salty to most people when chloride levels reach about 250 mg/L. The EPA recommends that sodium levels should be less than 20 mg/L.

Salt has infiltrated 3 of Madison’s 22 drinking water wells:

Well 14 on University Ave has shown the most dramatic rise in salt levels. In 2023, sodium measured 71 mg/L, exceeding EPA guidelines.
Well 16 on Mineral Point Rd and Well 6 on University Avenue also have rising salt levels. They are in danger of exceeding the EPA's sodium recommendations.

Health Concerns

Sodium levels can be a concern for people on low-sodium diets. Visit the WI Department of Health for more information.
Public Health Madison & Dane County (PHMDC) has issued a report on sodium in drinking water.
If you have questions about sodium in drinking water, reach out to your health care provider.
Elevated chloride does not affect human health.

Water Quality Reports

Annual Drinking Water Quality Report, Madison Water Utility
Water quality for wells that serve my address