Fourmile Lake is a 256-acre waterbody located in the Chelsea State Game Area of Michigan, approximately one mile north and two miles east of Chelsea. The lake features a small gravel boat launch on its south end, suitable for small watercraft and paddlers. The lake is characterized by shallow water, with over 75% of its surface area less than 5 feet deep and a maximum depth of 18 feet.

The shoreline is largely undeveloped, with only about 10 seasonal and year-round homes on the east side. The remainder of the shoreline is low and marshy, surrounded by state land. Recent reports indicate launching conditions have become increasingly challenging, with the lake becoming shallower even after heavy rains. The launch area is best suited for kayaks and small utility boats.

Abundant aquatic vegetation includes coontail and broad-leaf pond weed as the dominant species, with Eurasian milfoil, bulrush, and pond lily also present. Cattails are prominent along the southern and western shores. This vegetation, combined with the shallow depth, can affect paddling conditions throughout the lake.

The lake has historical significance as a former marl mining site, with several "marl pits" located just south and west of the main lake. A cement plant once operated on the south end. These adjacent ponds cover approximately 60 acres and are accessible by trails.

Wildlife observers may spot waterfowl, particularly in fall when hunting blinds dot the shoreline. The lake experiences seasonal water level fluctuations, managed by a water control structure that maintains a legal lake level of 887.0 feet above sea level.

The lake's gradually sloping bottom and extensive shallow areas make it particularly susceptible to wind effects, an important consideration for paddlers planning trips.