Grand Lake St. Marys, Ohio, USA

Also known as:  Grand Lake

Welcome to the ultimate guide to Grand Lake St. Marys — things to do, where to stay, fun facts, history, stats and more. Let’s dive in!

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All About Grand Lake St. Marys

Lake Locations: USA - US Midwest Region - Ohio - Northwest Ohio -

With its sail billowing in the wind, the sailboat glides in front of the lighthouse. It’s a rare scene for an inland lake, but Grand Lake St. Marys is a rare lake. Three lighthouses grace the lake’s shores. The north shore’s Northwood Lighthouse was constructed in 1923 and is on the National Register of Historic Places. It is only visible by boat. Grand Lake’s lighthouses, however, aren’t the only reason to take to the water. The lake in northwest Ohio stretches nine miles long with plenty of water for boating, and the fishing is exceptional year round.

Grand Lake St. Marys was created as a storage reservoir for the Miami and Erie Canal. Known as a canal feeder lake, it is one of several reservoirs that were used to keep water levels stable and maintain the canal’s five foot depth. Construction of Grand Lake was started in 1837 and completed in 1845. At the time of its completion, it was the largest manmade reservoir in the world. Today, it is still the largest inland lake in the state of Ohio.

With an average depth of just six feet and the majority of the lake under seven feet deep, Grand Lake St. Marys is a shallow lake. Its 12,900 acres sprawl across parts of Auglaize and Mercer Counties. Grand Lake is an impoundment of Coldwater Creek, and its outflow is Beaver Creek. Part of the lake’s 74 mile shoreline is in the Grand Lake St. Marys State Park. Established in 1949, it is one of Ohio’s oldest state parks.

The Grand Lake St. Marys State Park includes a campground with RV sites and cabins. There is a beach for swimming and several public boat launches. A state wildlife refuge on the southwest corner of Grand Lake provides a stopping place for migratory birds and waterfowl including Canada geese, grebes, swans, egret, loons and cormorants. Several pairs of nesting bald eagles make their home in the refuge. The Ohio Department of Natural Resources (DNR) holds a lottery for the many duck blinds along the lakeshore during hunting season. Only a mile and a half from the state park, the 47 mile long Miami-Erie Trail, part of the Buckeye Trail, provides an opportunity to hike across the state.

In the past, walleye were stocked in Grand Lake St. Marys, and there are abundant populations of largemouth bass and black and white crappie. In the winter, the yellow perch fishing is exceptional. Anglers can compete in several fishing tournaments held on Grand Lake throughout the year. The St. Mary’s Fish Hatchery is on the eastern shore of the lake. It produces saugeye, walleye, channel catfish and bass that are stocked in lakes across the state.

In addition to the public facilities maintained by the state park, there are several private marinas with boat launches, fuel and boat rentals. After a day on the water, fishing, boating or water skiing, guests can relax at one of Grand Lake’s waterfront restaurants before retiring to one of the vacation rentals, cottages or bed and breakfasts. The town of St. Marys has any additional amenities a visitor might need including real estate for sale for those wishing to extend their stay. A short drive from Grand Lake St. Marys, Wapakoneta’s Armstrong Air and Space Museum is dedicated to Ohio’s native son and the first man to set foot on the moon: Neil Armstrong. The museum includes the Gemini VIII aircraft and artifacts from the Apollo 11 mission and is sure to awaken the inner space explorer in anyone.

The rich history, spacious water, and abundant fish combine to make Grand Lake St. Marys a rare treat and a fantastic Ohio destination.

Lake Updates:

May 19, 2011: Warning signs are once again being posted. Toxic blue-green algae have returned to the lake. Alum treatment has been delayed to June due to heavy spring rains.

April 2011: Optimism is high for this summer’s recreation. State agencies will treat the lake with alum and hydrogen peroxide to lock up phosphorous feeding the algae, dredging phosphorus-rich sediment, and creating wetlands to intercept farm runoff.

February 7, 2011: Ohio’s Environmental Protection Agency lifted the advisory against eating fish caught from Grand Lake St. Marys. The EPA tested channel catfish, largemouth bass, crappie, and bluegill collected from the lake last fall.

October 29, 2010: Grand Lake St. Marys is no longer under a toxin advisory. Although state offficials declared the lake safe for recreation, advisories against fish consumption remain.

Health Alert, Summer 2010: Officials posted warning signs around the lake due to blue-green algae, known as cyanobacteria, that have made the lake unsafe for swimming, boating, and fishing. Algae feed on fertilizer and manure runoff from nearby farms that flow into streams that empty into the lake. Ohio’s governor announced a series of steps, starting in September, to combat the algae outbreak.

Things to Do at Grand Lake St. Marys

  • Vacation Rentals
  • Fishing
  • Fishing Tournaments
  • Boating
  • Sailing
  • Swimming
  • Beach
  • Water Skiing
  • Camping
  • Campground
  • Cabin Rentals
  • Hiking
  • Hunting
  • Wildlife Viewing
  • Birding
  • State Park
  • Museum

Fish Species Found at Grand Lake St. Marys

  • Bass
  • Black Bass
  • Bluegill
  • Catfish
  • Channel Catfish
  • Crappie
  • Largemouth Bass
  • Perch
  • Saugeye Perch
  • Sunfish
  • Walleye
  • White Crappie
  • Yellow Perch

Find Places to Stay at Grand Lake St. Marys

If you’re considering a Grand Lake St. Marys lake house rental or hotel, we’ve made it super easy to find the best rates and compare vacation accommodations at a glance. Save time using this interactive map below.

Recommended Sites to Book a Grand Lake St. Marys Vacation

If you want to take a deeper dive to find waterfront lake cabins, cottages, condos, hotels or resorts, check out our favorite Grand Lake St. Marys lodging partners.

  • VRBO – Use VRBO to find the perfect lake rental home, condo, cabin, cottage or other vacation property.
  • – One of the world’s leading digital travel companies, connects travelers to everything from cozy B&Bs to luxury resorts.
  • Expedia – Expedia is a popular online travel agency with more than 140,000 lodging properties worldwide.
  • – With more than 325,000 hotels in 19,000-plus locations, is an industry leader in online accommodations.
  • TripAdvisor – Read traveler reviews and compare prices on hotels, vacation rentals and more at TripAdvisor.
  • Trivago – Trivago helps travelers compare deals for hotels and other accommodations from a variety of booking sites.
  • KAYAK – KAYAK scours hundreds of other travel websites at once to find the best deals on hotels and other travel-related services.
  • RVshare –RVshare connects travelers interested in renting a motorhome with owners who have RVs to rent.
  • CampSpot – Campspot offers premier RV resorts, family campgrounds, cabins and glamping options across North America.

Note: These are affiliate links so we may earn a small commission if you book through them. While there is no extra cost to you, it helps provide resources to keep our site running (thank you)! You can read our full disclosure policy here.

Grand Lake St. Marys Statistics & Helpful Links


Lake Type: Artificial Reservoir, Dammed

Water Level Control: Ohio Dept. of Natural Resources

Surface Area: 12,900 acres

Shoreline Length: 74 miles

Normal Elevation (Full Pond): 871 feet

Average Depth: 6 feet

Maximum Depth: 16 feet

Completion Year: 1845

Trophic State: Hypereutrophic

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