Prairie fens are peat-covered wetlands that are often springy when walked upon. These fens are fed by a constant flow of mineral-rich groundwater that seeps to the surface and flows through and over the accumulated peat. The groundwater, rich in both calcium and magnesium, contributes to the alkaline soil condition.

Historically, dry upland communities such as mixed oak savannas were subject to fire, which also burned into the adjacent prairie fens. Plants found in fens are adapted to alkaline soils, periodic fire, and a constant flow of cool groundwater.

Typical plants in a prairie fen are big bluestem, Indiangrass, tamarack, shrubby cinquefoil, bog birch, poison-sumac, and many species of sedges and rushes. The extremely alkaline soils limit the variety of plants found in fens, but alkaline-tolerant plants like grass-of-Parnassus, Kalm's lobelia, round-leaved sundew, and pitcher plant may be found. Prairie fens also harbor a number of rare plant species, including Indian plantain, white ladies'-slipper, common valerian, prairie dropseed, and rosinweed.

A number of animals make their homes in or around fens. The Mitchell's satyr butterfly, a federally endangered species, is one of the more special finds in the fens of southwest Michigan. Other common finds are dragonflies, water snakes, and turtles.

There are 85 known prairie fens in Michigan, totaling about 2,000 acres. Although prairie fens are not considered to be globally imperiled, they are often found only in very small, isolated pockets, and good quality sites can be very difficult to find. In the southern Lower Peninsula of Michigan, prairie fens occur primarily in areas with a lot of topographic relief.