Fourth Lake and its fen ecosystem are home to a variety of state threatened and endangered plant species and could provide habitat for the American bittern and various rails.
Fens are rare, often sloping, wetlands that occur where mineral rich alkaline groundwater comes to the surface. Unlike bogs, fens have higher nutrient and mineral levels and sustain a more diverse plant and animal community. Fens are often covered by grasses, sedges, reeds and wildflowers.
Considered a swale, rather than a kettle ecosystem, the fen is situated between two ridges of the Valparaiso Moraine. The fen drains south into Fourth Lake, which drains eastward via Mill Creek to the Des Plaines River.
The preserve offers a short 0.3-mile grass loop trail with a scenic overlook near the lake. In addition, a 2.7-mile gravel section of the Millennium Trail stretches through Fourth Lake from just north of Rollins Road to Sand Lake Road where it connects to the existing trail at Bonner Farm and McDonald Woods in Lindenhurst. Please keep dogs leashed and on trails at all times, and pick up after them