Its primary inlet is the Pentwater River; its outlet is a man-made channel flowing into Lake Michigan.

Pentwater Lake has a surface area of 431 acres (174 ha), a maximum depth of 50 feet (15 m), and an average depth of 27 feet (8.2 m).

The lake contains 11,590 acre-feet (14,300,000 m3), a volume of water that would cover 18 square miles (47 km2) to a depth of 1 foot (0.30 m).

Its shoreline is 6.2 miles (10.0 km) long.

This Oceana County, Michigan location article is a stub.