Mary Lake State Natural Area

About Us

The 3-acre Mary Lake is one of very few known meromictic lakes in Wisconsin. Meromixis, the permanent thermal stratification of the water, results from the lake having an extremely small surface area in comparison to its depth. Mary Lake has a small 3-acre surface area but is disproportionately very deep - 67 feet. Due to the extreme relative depth in relation to surface area, watershed soils, and its protection from surrounding uplands, Mary Lake never "turns over" and circulates as the water temperature changes in the spring and fall as is typical of most other Wisconsin lakes. Instead, the lake stays stratified creating unusual chemical and biological layers. Internationally known to limnologists, extensive research has been conducted on the physical, biological, and chemical properties of the lake since the 1920's.

Mary Lake is second in a chain of five interconnected lakes and is primarily fed by land runoff and inflow from a small stream that connects Mary Lake to nearby Lake Rose. Mary Lake is nestled in a small basin and surrounded by dense forest, which helps shelter the lake from wind action. The surrounding forest is primarily second-growth northern hardwood forest, swamp hardwoods, and swamp conifers. Dominant species include white cedar, spruce, white pine, and balsam fir. Mary Lake is owned by the DNR and was designated a State Natural Area in 1999.