[4] As the Laurentide Ice Sheet began to retreat from present-day Northern Indiana and Northwest Ohio between 14,000 and 15,000 years ago, it receded into three distinct lobes.

Around 11,000 years ago the waters of Lake Maumee became deep enough that it breached a "sag" or weak spot in the Fort Wayne Moraine.

This caused a catastrophic draining of the lake, which in turn scoured a 1 to 2 mi (1.6 to 3.2 km) wide valley known as the Wabash-Erie Channel or "sluiceway".

[5] When the ice melted completely from the region, new outlets for Lake Maumee's water opened up at elevations lower than the Wabash-Erie Channel.

It is not known for certain when, but at some point in the distant past the St. Joseph and St. Marys Rivers jumped their banks and flooded the marshy ground of the Fort Wayne Outlet.

[6] The Wabash was first mapped by French explorers to the Mississippi in the latter half of the 17th century, including the sections now known as the Ohio River.

[7] In the 18th century, the profitable 8-mile portage between the Maumee River and the Wabash was controlled by the Miami people at Kekionga.

A 329-acre (133 ha) remnant of the old-growth forests that once bordered the Wabash can be found at Beall Woods State Park, near Mount Carmel, Illinois.

A half mile downstream (i.e. east), at a roadside park on Ohio 49 at the Mercer County line, is a historical marker that announces the river's start.

Between the start of the river and Fort Recovery, the current is swift and the water remains very shallow and follows a poorly defined channel.

The shallow depth and low bridge clearances make the section nearly impassable by boat except in the most ideal conditions.

The canals were abandoned after competing railroads took over; this allowed the river to shift courses several times, resulting in the formation of many cut-offs and coves with no outlet.

An additional seventeen tributaries raise the depth of the river considerably, making it navigable for larger vessels.

[14] At mile fifty-nine, the river passes through Ouabache State Park, where it begins to widen and become more shallow.

[14] As the river exits the park and flows toward the city of Bluffton near mile sixty-six, it widens further, becoming more shallow; only a narrow channel is navigable by larger vessels.

The river remains shallow and somewhat rocky with minor rapids until mile seventy-one near the community of Murray.

Built by the Army Corps of Engineers to make a reservoir, the dam creates the J. Edward Roush Lake.

As the river passes Wabash and moves toward Peru, it splits, creating a series of islands; sandbars are common in the stretch.

[20] Although navigable by large ships in the past, the remainder of the river becomes shallow in places due to erosion and silt.

It borders Illinois beginning at mile 316, and serves as a state boundary line with Indiana for the remainder of its course.

[21] South of Darwin, beginning at mile 410 a large bluff gradually rises, eventually towering two-hundred feet over the river.

Past Vincennes, the Wabash is joined by its largest tributary, the White River at Mount Carmel, Illinois, significantly increasing its size, to over 750 feet wide.

Roughly a mile downstream, near the Gibson Generating Station, another large tributary, the Patoka River, also joins.

From the tail southward there are several cut-offs from the river, resulting in several natural exclaves between Indiana and Illinois, the largest of which is at Grayville.

The Little Wabash River, another major tributary, joins at mile 482 on the Illinois side, near New Haven.

A number of amphibians occur throughout the river's watershed including the American bullfrog and the eastern newt.