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Grand Lake St Marys State Park

Originally constructed as a feeder reservoir for the Miami & Erie Canal, Grand Lake St. Marys was the world's largest reservoir when built. Today, Grand Lake St. Marys State Park offers 52 miles of shoreline for boating and fishing, as well as a large campground, picnic areas, and a swimming pool.



The 13,500-acre lake allows unlimited horsepower. A 300-foot no-wake zone has been established and is enforced around the lake’s 52 miles of shoreline.

Eight state-operated launch ramps provide access to the lake. Several private launch ramps also exist along the shallow shoreline. Seasonal dock rentals are available, call the park office for information.

The state wildlife refuge, located on the southwest corner of the lake, is off limits to boats at all times.


Grand Lake St. Marys Campground offers Cedar Cabins and Camper Cabins as well as Full Hook-up, Electric, and Non-electric sites for every type of camping. Pets are permitted in most areas and a dog park is located in the campground. Other amenities include pool, splash pad, boat launch. Reservations are required and can be made up to 6 months in advance, online or by calling (866) 644-6727.

Dog Parks

Two dog parks are available. On the East Bank is the Fur-Ever Friends Dog Park. On the West Bank is the Celina Rotary Dog Park. Both offer a place for your dog to frolic without a leash. The campground also offers a dog park for registered campers only.


Largemouth bass, white and black crappies, bluegills, walleye, channel and flathead catfish, yellow perch, bullheads and carp are found in the lake. Gizzard shad is the primary forage species for predators.

Download the Fishing Map


Limited hunting is permitted in designated areas.

Download the Hunting Map


Several picnic areas with tables and grills are located in scenic areas around the lake on a first-come, first-served basis. Some are covered.

Reservable Shelterhouses

Four shelterhouses that can be reserved online or by calling (866) 644-6727.


Four public swimming beaches are available. Swimming is permitted during daylight hours only. Visitors swim at their own risk. Pets are not permitted on swimming beaches. Other swimming areas are also provided for boaters.

  • BeachGuard — Water quality advisories, Memorial Day to Labor Day, from Ohio Dept. of Health


Three trails are within the park.

  • West Bank Multi-use Trail  1.2 miles  Easy  paved, accessible
  • East Bank Multi-use Trail 1.4 miles  paved, accessible
  • Red Wing Hiking Trail - 0.65 mile (campground)

Visitors may also hike down to the canal feeder junction near the historic Miami and Erie Canal to the Miami-Erie Trail, Buckeye Trail, and North Country Scenic Trail.

Winter Recreation

Under the proper conditions, park visitors can enjoy snowmobiling, ice fishing, and cross-country skiing.

More to Do

  • Playground 
  • Naturalist programming is seasonal 
  • Camp Store in the campground offers snacks, ice, souvenirs

History & Natural Features


The area in and around Grand Lake St. Marys State Park played an important part in the development of the Northwest territory. The St. Marys River served as a vital link between the Great Lakes and the Ohio River. Because of this heavy water traffic, the renegades Simon and James Girty established a trading post, which eventually evolved into the town of St. Marys.

General “Mad” Anthony Wayne passed through the area in 1794 during his march to drive out the Shawnee, which culminated in the Battle of Fallen Timbers. Some of Wayne's men returned here to make their homes.

In 1837, work commenced on a reservoir for the Miami-Erie canal to maintain the canal’s 5-foot water depth. Workers using hand tools were paid 35 cents a day and a jigger of whiskey to keep malaria away. At its completion in 1845, 13,500-acre Grand Lake was the largest man-made lake in the world. The lake was connected to the canal by a 3-mile feeder.

The canal prospered until the advent of the railroads in the 1870s. The area experienced another boom in the late 1890s when oil was discovered. For a time the lake was dotted with oil derricks. Today a pile of rocks near the center of the lake marks the spot of the last producing well. Download a map of Historic Oil and Gas Wells in and Adjacent to Grand Lake St. Marys.

Grand Lake St. Marys and other canal feeder lakes in the state were the first areas to be dedicated as Ohio state parks in 1949.

Natural Features

At one time, the vast expanse of water that is Grand Lake St. Marys was a vast wet prairie and forests that stretched from the Allegheny Mountains of Pennsylvania to the prairies of Illinois. In addition to forests, pre-settlement Ohio contained large prairies and wetlands. Today, the park contains varying habitats including woodlands, wetlands, and prairies in addition to the surrounding croplands.

Grand Lake St. Marys was the site of the first offshore oil drilling in the world. Between 1891 and about 1913, over 100 oil wells had been installed and operated over the waters of the lake. It took the discovery of greater oil reserves in Texas to put an end to Ohio’s oil boom. Download The Geology of the St. Marys Region booklet.

Perfect for bird enthusiasts, Grand Lake St. Marys lies along one of the country's major migration routes. Many birds use the lake as a resting stop and nesting area, including Canada geese, ducks, grebes, swans, egrets, loons, herons, cormorants and ospreys. Bald eagles, magnificent birds long absent from the area, have begun nesting on the southwest corner of the lake at the wildlife refuge. Other animals of the park include fox, squirrel, mink, raccoon, beaver, coyote, white-tailed deer, and many others.

Lake Improvement Association for Grand Lake St. Marys


Call: 911

Phone Number

(419) 394-3611



Natural Features