Caroline Lake is an undeveloped soft-water drainage lake and the headwaters of the Bad River, which eventually replenishes the water of the National Natural Landmark, Kakagon/Bad River Sloughs. While important primarily for its position at the headwaters of the Bad River, the lake is surrounded by numerous high quality plant communities including northern wet forest, northern dry-mesic forest, northern sedge meadow, shrub carr, and open bog. Lakeshore vegetation is predominantly upland hardwoods with a mixed conifer, hardwood and tag alder swamp near the Bad River outlet and along the northeast shore on an intermittent feeder stream. A narrow zone of macrophytes occupies a 1 to 15 meter wide strip along much of the shoreline. Representative species are hard-stem bulrush, river horsetail, water-shield, bull-head pond-lily, white water-lily, ribbon-leaf pondweed, and coon's-tail. Fresh water sponges have been observed near the outlet on submerged woody debris. The nearby Twin Lakes-East is a soft-water seepage lake with a short, navigable stream channel connecting to Twin Lakes-West. Bog vegetation surrounds Twin Lakes-East on its west and eastern shores. Upland hardwoods and conifers are also present. Twin Lakes-West is an acid bog lake with an outlet flow to the northwest to Eureka Lake. Black spruce, tamarack, birch, red maple, and white pine surround the lake. Upland areas contain scattered red and white pine. The extensive forested wetlands of this site are an important nesting area for several warbler species. Common loons, osprey, and bald eagles have been observed at the site. Caroline Lake is owned by The Wisconsin Chapter of the Nature Conservancy and the DNR. It was designated a State Natural Area in 2002.