Grand Lake St. Marys State Park is a public recreation area located on Grand Lake in Mercer and Auglaize counties, Ohio. Grand Lake is the largest inland lake in Ohio in terms of area, but is shallow, with an average depth of only . The state park is open for year-round recreation, including boating, fishing, swimming and hunting. The park consists of the lake and park facilities scattered all around the shore intermingled with private property and a facility operated by Wright State University. It is west of St. Marys, and southeast of Celina, southwest of Lima in the northwestern part of the state. History Grand Lake St. Marys was constructed in the early 19th century as a reservoir for the Miami and Erie Canal, which connected the Ohio River with Lake Erie. At one time the lake was the world's largest man-made lake. The canal system thrived for about thirty years in the mid-to-late 19th century before it was replaced by the railroads. In the 1890s oil was discovered in the area, and oil derricks were set up in the lake sometime around 1891. This made Grand Lake the location for the first off shore oil drilling to take place. The lake became one of Ohio's first state parks in 1949 with recreational facilities built in the following years. Names The official geographic name of the lake is Grand Lake. The United States Geological Survey Board of Geographic Names disapproved a proposal to change the name Grand Lake to Grand Lake-Saint Marys, which is the name given on state maps and documents. The 1920 edition of the Encyclopædia Britannica shows the name as Lake Mercer on the map of Ohio in the article on Ohio. "Lake St. Marys" was a name introduced in the early 1900s and wasn't popular with Celina residents. The body of water has also been referred to as "Grand Reservoir" and "Lake Celina" among other names. Ecology The land on which Grand Lake St. Marys is located was once part of a forest that stretched from the Appalachian Mountains in Pennsylvania to the prairie in Illinois. Much of the forest was cleared by pioneer farmers as the area was settled in the years following the Northwest Indian War. The forests have been replaced by farmland with fields of wheat, soybeans, and corn. Grand Lake St. Marys was once a swampy prairie. When the lake was