Grand Lake St. Marys is located in west central Ohio. The city of St. Marys is located near the northeast corner of the lake and Celina is on the northwest corner.
The lake is approximately 9 miles long and 3 miles wide. The prevailing westerly winds commonly create whitecaps; strong winds can create dangerous wave conditions. Small boat operators should exercise extreme caution when traveling across the lake.
Ohio State Parks operates and maintains 7 boat ramps, a marina with rental boats, seasonal rental docks, two swimming beaches, picnic areas and picnic shelters, handicap accessible shoreline fishing piers, and a campground in Grand Lake St. Marys State Park.
- Check for water quality advisories
History
Grand Lake St. Marys was constructed from 1837 to 1845 to store water for the Miami-Erie Canal. Two earthen dams were built on the headwaters of two major drainage systems flooding the area between them. The spillway on the west end discharges water into the Wabash and Ohio River drainage systems; water from the east end spillway flows into the St. Marys River, and from there into the Maumee River and Lake Erie. The lake covers approximately 12,680 acres and is Ohio’s largest inland lake entirely within state borders.
Most of the lake is less than 7 feet deep with a soft bottom of silt. Some isolated areas of sandy or clay bottoms exist where wave action keeps the bottom cleaner. Lots of rock rip rap has been added to reduce shoreline erosion; these rocky shorelines provide cover for several species of fish. Numerous boat docks, shoreline brush, and fallen trees provide cover for fish.
