Lake Agassiz

Lake Agassiz was a vast proglacial lake that occupied parts of central North America during and after the last Ice Age. It is a geological feature rather than a present-day lake and is known for its large extent and influence on continental drainage.

At its largest phase the lake covered a very large area across what are now southern Manitoba and neighbouring parts of Ontario, Saskatchewan and the north-central United States. Its outflows and catastrophic drainage events changed river courses and contributed freshwater pulses to the North Atlantic during deglaciation.

The lake formed as the Laurentide Ice Sheet retreated, accumulating meltwater behind ice margins and moraines. It persisted through multiple stages and outlet shifts before finally disappearing as modern drainage systems established in the early Holocene.

Remnants of Lake Agassiz are now the low-lying plains and lake basins of central Canada and adjacent U.S. states, including modern lakes, wetlands and fertile prairie soils.

• Peak extent: At its maximum extent it covered a vast area of central North America, making it one of the largest proglacial lakes known on Earth.
• Origin and drainage: Formed as the Laurentide Ice Sheet melted after the Last Glacial Maximum and existed during the late Pleistocene and early Holocene, with major drainage events that affected regional hydrology and ocean circulation.