Grand Lake St. Marys State Park centers on Ohio’s largest inland lake by area, a shallow water body created in the early nineteenth century as a reservoir for the Miami and Erie Canal linking the Ohio River and Lake Erie. Once regarded as the world’s largest man-made lake, it later shifted from canal infrastructure to recreation and became one of Ohio’s first state parks in 1949. The lake also holds an unusual place in industrial history as the site of the first offshore oil drilling after nearby discoveries in the 1890s. Today it supports varied recreation, wildlife habitat, and fish stocking, even as runoff, sewage, siltation, and development have harmed water quality.