Grand Lake St. Marys in western Ohio is the state's largest inland lake, offering 13,500 acres of paddling opportunities. The lake is approximately 9.5 miles long with 52 miles of shoreline. Eight state-operated launch ramps provide access around the lake. Paddlers can enjoy scenic tree-lined shores, with the north shore featuring well-kept yards and channels, while the south shore offers more natural habitat.

Wildlife viewing is a highlight, with opportunities to spot nesting bald eagles, blue herons, egrets, and various duck species. The lake's shallow depth makes it prone to rough conditions during storms, so paddlers should exercise caution and be prepared to seek shelter in the numerous channels and creeks.

No wake zones extend 300 feet from shore. The state wildlife refuge in the southwest corner is off-limits to all boats. Ohio requires boat registration for all watercraft. Several public beaches and picnic areas with tables and grills are available around the lake.

The lake was originally constructed as a feeder reservoir for the Miami & Erie Canal and was once the world's largest man-made lake. Oil derricks once dotted the lake during a late 1890s oil boom. Today, Grand Lake St. Marys State Park offers camping, hiking trails, and other amenities for paddlers looking to extend their visit.

Fall foliage makes autumn an especially scenic time to paddle. The annual Celina Lake Festival in late July features numerous water activities. Paddlers should be aware that the lake has experienced water quality issues in recent years, so checking current conditions is advisable before planning a trip.