The Great Black Swamp, or simply Black Swamp, was a glacially caused wetland in northwest Ohio, United States, extending into extreme northeastern Indiana, that existed from the end of the Wisconsin glaciation until the late 19th century.
Comprising extensive swamps and marshes, with some higher, drier ground interspersed, it occupied what was formerly the southwestern part of Glacial Lake Maumee, a holocene precursor to Lake Erie.The area was about 40 kilometres (25 mi) wide (north to south) and 160 kilometres (99 mi) long, covering an estimated 4,000 square kilometres (1,500 sq mi). Gradually drained and settled in the second half of the 19th century, it is now highly productive farm land.
Its historical boundaries lie primarily within the watersheds of the Maumee, Auglaize, and Portage rivers in northwest Ohio. The boundary was determined primarily by ancient sandy beach ridges formed on the shores of Lakes Maumee and Whittlesey, after glacial retreat several thousand years ago. It stretched roughly from Fort Wayne, Indiana in the west, to Sandusky, Ohio on the east, and from the Maumee River valley south to near Findlay, Ohio and North Star, Ohio.
Near its southern edge at the southwestern corner of present-day Auglaize County, the swamp was so impervious to travel that wheeled transportation was impossible during most of the year, and local residents thought the rigors of travel to be unsuitable for anyone except adult men.
The area was not continuous swamp, but rather characterized by a variety of vegetation types (Sampson, 1930; Kaatz, 1955). In the lowest, flattest areas, prone to permanent inundation, deciduous swamp forests predominated, characterized especially by species of ash, elm, cottonwood and sycamore. In slightly higher areas with some topographic relief and better drainage, beech, maples, basswood, tuliptree and other more mesic species were dominant.
On elevated beach ridges and moraines with good to excessive drainage, more xeric species, especially oak and hickory, were dominant. Unlike other swampy areas of the Great Lakes, such as northern Minnesota, there were no conifers (Sampson, 1930).
The area contained non-forested wetlands, particularly marsh and wet prairies, with marshes being particularly extensive along the Lake Erie shoreline between Toledo and Sandusky. Some of these exist today in modified form in state and federal wildlife refuges, such as the Ottawa National Wildlife Refuge.