Grand Lake St. Marys originated as the Grand Reservoir for the Miami and Erie Canal and was later known variously as St. Marys, Lake Mercer, or Grand Lake before the name Grand Lake St. Marys came into use. Its creation grew from Ohio’s early canal ambitions after New York Governor De Witt Clinton contacted Ohio Governor Ethan Allen Brown in 1820 about a canal system that would connect Lake Erie and the Ohio River, open Ohio’s interior to transportation and settlement, and support the farm economy. After canal routes were surveyed, the Ohio Canal began on July 4, 1825, in Licking County, the Miami Canal was built from Cincinnati to Middletown and extended to Dayton by 1837, and the Miami and Erie Canal continued north toward Lake Erie. Because that extension required feeder reservoirs to maintain water levels, construction of the Grand Reservoir is estimated to have begun in 1837, though records of the actual start are poor. Financed by state and private money, the reservoir was considered complete with the east bulkhead in 1845 at a cost of about $529,000, although the canal system never became a profitable investment. Historic data gives the reservoir’s original size as 17,000 acres, while it is now estimated at 13,500 acres; it is 8.33 miles long, 3.79 miles wide at its widest point, has more than 40 miles of shoreline, and averages 8 feet in depth. When created in the 1840s, it was the largest man-made lake in the world, a distinction it held well into the twentieth century, and it remains notable as one of the few large lakes created by embankments at both ends. The reservoir was built in a low, poorly drained swamp near the canal route, where surveyors realized that raising the east and west ends would impound enough water; they cleared the land between, diverted Coldwater Creek into the basin, removed loamy soil beneath the embankments until reaching clay, and built the levees from hauled clay. Construction was laborious hand work or done with scoops pulled by horses, mules, or oxen, and an estimated more than 1,500 men, many of them German and Irish immigrants, built the reservoir, with many later settling in the surrounding area.