03/28/2026
Look at northwest Ohio in LIDAR.
This is the footprint of the Great Black Swamp.
It’s a broad, smooth basin surrounded by faint ridges. That landscape didn’t start as a swamp. It started as the bottom of Glacial Lake Maumee, an early version of Lake Erie.
When the water drained away, it didn’t leave hills behind. It left a flat floor.
That flat, poorly drained surface is what allowed the swamp to form.
Those faint arcs around the edges are moraines that served as old shorelines, still visible in the land. Some of today’s roads still follow them, because before drainage, they were the only dry ground.
Even now, the rivers are slow and the drainage is poor. This was the Great Black Swamp.
Source: USGS National Map Viewer (public domain) via Wikimedia Commons (GeoFAXsafety79)