Grand Lake St. Marys is a large artificial lake located in Mercer County, Ohio. Created in the 1840s to provide water for the Miami and Erie Canal, it covers approximately 13,500 acres, making it one of the largest inland lakes in the state. The lake is surrounded by parks and recreational areas, offering various activities such as fishing, boating, and hiking. The lake is also home to diverse wildlife and serves as an important habitat for many species. Grand Lake St. Marys State Park provides facilities for camping and picnicking, attracting visitors year-round. The area is known for its scenic beauty and outdoor recreational opportunities.