Lake St. Helen is a 2,400-acre (9.7 km²) public lake located in Roscommon County in the U.S. state of Michigan, and borders on the community of St. Helen, Michigan. It is the headwaters for the south branch of the Au Sable River. From 1998 to 2003, the Lake was subject to a water weed (millfoil) eradication project, involving weevil restocking, which was successful at the time. Fishing is available throughout the lake, albeit different fish are found in different places, and includes: bass, bluegill, brown trout, crappie, lake trout, perch, pike, rainbow trout, smallmouth bass, and walleye.