Mentor Marsh is an 850 acre Lake Erie wetland formed from the abandoned channel of the nearby Grand River and a large portion of it is protected as a State Nature Preserve (SNP). Mentor Marsh SNP was one of the first four State Nature Preserves designated in Ohio and is locally managed and co-owned by CMNH Division of Natural Areas.

It provides critical spawning habitat for Lake Erie fish and is an important refuge and nesting site for waterfowl and migrating songbirds; more than 200 species of birds have been recorded using the site, including several state listed species.

The Mentor Marsh Carol H. Sweet Nature Center at is a good place to learn about the natural history of the area and to start your Marsh visit. Hands-on activities, displays and information help tell the Marsh story. Mentor Marsh's three trails are open from dawn to dusk, year-round.