Grand Lake in Ohio

Once the world's largest man-made lake, Grand Lake in the UNITED STATES OF AMERICA is the state of Ohio's largest inland lake and is approximately 20 miles east of Indiana. Located in western Ohio, the artificial lake lies mostly in eastern Mercer County but also western Auglaize County. The original purpose of establishing the 13,500-acre lake in the year 1837 was for it to be a feeder reservoir to supply water for the Miami-Erie Canal. Like other feeder reservoirs for canals, Grand Lake is quite shallow with an average depth of 4 feet. A lake map from GoFishOhio.com (link opens in new tab or window) reveals the deepest depth at only slightly above 10 feet. Grand Lake is surrounded by the Grand Lake St. Marys State Park, operated by the Ohio Department of Natural Resources and featuring a campground on the northeast side. Unfortunately, the ODNR discourages swimming in the lake - especially in regards to children, the elderly, and people with illnesses - because excessive algal blooms are releasing excessive toxins. Regardless, recreational boating and offshore activities are still possible. Communities surrounding Grand Lake include New Bremen, New Knoxville, and Saint Marys in Auglaize County and Celina, Coldwater, and Montezuma in Mercer County.