Glacial Lake Maumee was a proglacial lake that was an ancestor of present-day Lake Erie. It formed about 14,000 years ago. As the Erie Lobe of the Wisconsin Glacier retreated at the end of the last ice age, it left meltwater in a previously existing depressional area that was the valley of an eastward-flowing river known as the Erigan River that probably emptied into the Atlantic Ocean following the route of today's Saint Lawrence River. Some geologists (see M.C. Hansen, references below) think that the Erigan could have been a downstream segment of the preglacial Teays River system. The glaciers destroyed or disturbed most of the preglacial drainage patterns and enlarged and deepened the Erigan basin.
As the Erie Lobe retreated to the northeast, it left large debris deposits called moraines running at right angles to its line of retreat. One of these, called the Fort Wayne Moraine, was left at the site of present-day Fort Wayne, Indiana, where it acted as a dam that held back the waters of the lake. When the water was at its highest point, about 800 feet above sea level (ASL) (244 m), it left beach ridges that later became the routes of trails and highways. During this stage, the waters of the lake, possibly in response to an advance of the ice front at the lake's eastern end, overtopped a "sag" in the Fort Wayne Moraine. This caused a catastrophic drainage of the lake known as the Maumee Torrent that scoured a one- to two-mile-wide outlet running southwest to the Wabash River known as the Wabash-Erie Channel.
Two later stages of Lake Maumee, (called the "Lowest" and the "Middle," in that order) had lower water levels because the retreating ice exposed an outlet lower than the Wabash-Erie Channel. The Lowest Maumee (elevation: about 760 ft (232 m) ASL) drained westward through the Grand River in Michigan and into Glacial Lake Chicago, an ancestor of present-day Lake Michigan. Another advance of the ice blocked that outlet, raising the lake level to about 780 feet (238 m) ASL, the stage known as the Middle Maumee. A new outlet called the "Imlay Outlet" formed that connected with an unobstructed segment of the Grand River farther west. There is enough uncertainty about this sequence that some authorities think that Middle Maumee might have preceded Lowest Maumee.
Fluctuations in water level continued through more stages (Akrona, 695 feet (212 m); Whittlesey, 738 feet (225 m) ASL; Warren and Wayne, 660–685 feet (201–209 m) ASL; and Lundy, 590–640 feet (180–195 m) ASL. This see-saw pattern continued until an eastern outlet opened at Niagara, establishing the drainage pattern of modern Lake Erie (569 feet (173 m) ASL). This involved the reversal of drainage in what is now northeastern Indiana and northwestern Ohio as the Maumee River outlet developed by capturing streams that formerly drained into the Wabash. The Great Black Swamp that once occupied much of the land between Sandusky, Ohio, and New Haven, Indiana, was a remnant of the bed of Glacial Lake Maumee. Geologists call the former lake bottom the Maumee Lacustrine Plain.