Lake Agassiz

The Ultimate Fishing Spot?
Last updated 12-31-2023.

See the lesson plan and worksheet developed to use with this essay.

     Lake Agassiz, named after Swiss geologist Louis Agassiz, was a 700-mile long by 200-mile wide lake that once covered much of Manitoba as well as parts of Ontario, Saskatchewan, Minnesota, and North Dakota.  It was formed about 12,000-13,000 years ago at the end of the Pleistocene Epoch during last two phases of the Wisconsin Glacial Age (Agassiz Project, 1996) as a result of the accumulation of glacial meltwater that was prevented from flowing northward by remnants of the Laurentide Ice Sheet (Ostlie & Faust, 1997).  The lake's depth and size varied as the climate periodically warmed and cooled, causing the glacial ice to alternately retreat and then advance and the lake to partially drain and refill. (MPCA, 1997). However,  many of the lake's primary boundaries are apparent from old shorelines such as the Campbell Beach Ridge in Manitoba (University of Manitoba, 1995) as well as the Blanchard and Herman beaches in North Dakota and Minnesota (Uphum, 1999). Where rivers entered the lake, extensive deltas formed. The most prominent of these were at the mouths of the Sheyenne River in North Dakota and the Assiniboine River in Manitoba. Outlet channels, such as the Glacial River Warren, which is now the Minnesota River Valley, cut prominent scars through the landscape that can still be seen today (Ostlie & Faust, 1997).

     Approximately 8000-8500 years ago, as the climate warmed further, the Laurentide Ice Sheet melted sufficiently to allow the lake to drain nearly completely to the north, eventually into Hudson Bay. Today, only Lakes Manitoba, Winnipeg, Winnipegosis (all in Manitoba); Lake of the Woods and Rainy Lake (on the Minnesota and Ontario border); Upper and Lower Red Lakes: and many smaller lakes throughout the region remain from this once huge inland sea (Minnesota DNR, 1997). The fertile soil of the Red River Valley on the Minnesota-North Dakota border is also a vestige of the clay-like silt that accumulated on the bottom of the lake (Agassiz Project, 1996).

     Lake Agassiz's approximately 4000-year lifespan coincided with the existence of such now-extinct animals as the giant beaver, woolly mammoth, mastodon, giant short-faced bear, and giant ground sloth (Zimmerman, 1996). It is believed that the earliest humans to inhabit North America (called Clovis Man after the town in New Mexico where their artifacts were first discovered) migrated across the Bering Strait from Siberia and entered what is now Canada and then the United States between 12,000 and 10,000 years ago. Their existence in the Lake Agassiz area has been documented by the discovery of characteristic spearheads called Clovis points (Manitoba Archaeological Society, 1998). Therefore, they probably hunted some of these species along the massive lake's shores. Many scientists believe that the extinction of these ice-age mammals may be linked to human hunting.  

     Were there fish in Lake Agassiz? As we say here in Minnesota, "You betcha!" According to Dr. K. W. Stewart, a Professor of Zoology at the University of Manitoba, fossil remains of only four fish species have been found in the former lake bed. However, based on the their current distribution, Stewart estimates that 34 of Manitoba's 86 total fish species entered the province through Lake Agassiz (personal communication, May 26, 2000). These species include goldeye, lake sturgeon, lake trout, northern pike, and walleye.  

     So . . . was Lake Agassiz the ultimate fishing spot? We'll never know. One thing is certain, however. Traveling back in time and exploring this giant lake and its shores would be the ultimate adventure!

To learn more about Lake Agassiz and the prehistory of the area it once covered, take a look at the following links: Long-Lost Lake Agassiz Offers Clues to Climate Change,
Glacial Lake Agassiz, Louis Agassiz, The Pleistocene, The Arrival of the Big Game Hunters, The First Americans, America's Stone Age Explorers, Folsom Traditions, The Midwestern United States 16,000 Years Ago, Minnesota Archaeology.


Agassiz Project (1996). Facts about Agassiz. University of Minnesota. Minneapolis, MN: Agassiz Project Home Page.

Department of Anthropology (1995). Lake Agassiz. Winnipeg, Canada: University of Manitoba.

Manitoba Archeological Society (1998). Palaeo Period. Winnipeg, Canada: University of Manitoba.

Minnesota Department of Natural Resources (1997). Agassiz Lowlands. Saint Paul, MN: Minnesota DNR.

Minnesota Pollution Control Agency (1997). Glacial Lake Agassiz and the Red River Valley. St. Paul, MN: MPCA. 

Ostlie, Wayne R. and Thomas M. Faust (1997).  An Assessment of Biodiversity in the Lake Agassiz Interbeach Area:  An ecoregion within the Great Plains. The Nature Conservancy Great Plains Program.  Minneapolis, MN.  Jamestown, ND:

Uphum, W. (1999). The Glacial Lake Agassiz. Fargo, ND: North Dakota State University Library.

Zimmerman, A (1996). Mass Extinctions of the Ice Age in North America. Iowa City, Iowa: University of Iowa.  Link no linger functions.

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Posted by Edmund Sass, Ed.D.
Professor Emeritus of Education
College of Saint Benedict/Saint Johns University
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