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Ecoregion Description

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Species Richness

# of Endemic Species


116: Laurentian Great Lakes

Major Habitat Type:

large lakes


Text modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment. Island Press, Washington, DC, USA. Text also provided by Mary Burridge and Nicholas Mandrak.


Canada; United States


Encompassing portions of southern Ontario and eight American states, this ecoregion is comprised of the watersheds of the five Great Lakes (Superior, Michigan, Huron, Ontario, and Erie).

Drainages flowing into:

Positioned between the Arctic drainages to the north and the Mississippi and Atlantic drainages in eastern North America, the entire system drains into the Atlantic Ocean—the majority of water by way of the Gulf of St. Lawrence. In all, this area contains approximately one-fifth of the Earth’s freshwater.

Main rivers or other water bodies:

Lakes Superior, Michigan, Huron, Erie, and Ontario form the Great Lakes. With a total surface area of 245,000 km2 these are the largest group of freshwater lakes in the world. Other large lakes in the ecoregion include lakes Nipigon, Nipissing, Simcoe, and Lake St. Clair. Numerous small rivers and streams, which often are segmented by barrier falls, flow into Lake Superior—the largest, deepest, and coldest of the five Great Lakes, and the largest temperate freshwater lake (in terms of surface area) in the world. Among the larger rivers feeding Lake Superior include the Nipigon, St. Louis, and Pigeon rivers. Large rivers draining Lake Huron include the Spanish, French, Mississagi, and Saugeen rivers. Among the rivers feeding Lake Erie are the Thames and Grand rivers in Ontario, the Detroit River between Michigan and Ontario, and the Portage River in Ohio. Main rivers draining into Lake Ontario are the Niagara, Moira, and Oswego rivers. Lake Ontario receives the entire outflow of the other four Great Lakes. The smallest of the Great Lakes, Lake Ontario is second only to Superior in average depth.


Until approximately 10,000 to 15,000 years ago the entire region was covered by glaciers associated with the Wisconsinan Age, and the basins of the Great Lakes were created by the movements and the erosional forces of these glaciers. This has resulted in gently rolling topography with elevations below 250 m across much of the landscape, although a few ranges along the northern and western border reach upwards of 600 m (McNab & Avers 1994).

Much of this region is underlain by the acidic, Archean bedrock of the Canadian Shield. Bedrock outcroppings are common, and may be covered with sandy to loamy till in the north, and a thin, acidic sandy till in the south. The glaciers that once covered this ecoregion left areas now mantled with thick deposits of glacial drift. Limestone and dolomite cliffs of the Niagara Escarpment extend from Lake Michigan’s northern shoreline, northeast to Manitoulin Island, and southward along the Bruce Peninsula to Niagara Falls. Lakes Erie and Ontario are underlain by Palaeozoic bedrock and have low relief with poorly drained depressions, morainic hills, drumlins, eskers, and outwash plains as a result of glaciation.


The effects of the Great Lakes on climate, commonly called “lake effect,”  influences average temperatures, extreme temperatures, and the amount and timing of precipitation. Lake effect snow is common across the region, ranging from 1800 to over 8000 mm in some parts (McNab & Avers 1994). Climate tends to be continental to modified continental. Because the prevailing winds move from west to southeast, Lake Superior, the westernmost lake, is also the coldest of the Great Lakes, and as a result has a less ameliorating effect on temperature than that of the other Great Lakes (Ricketts et al. 1999).

Freshwater habitats:

The five Laurentian Great Lakes comprise the largest freshwater ecosystem in the world, holding over 20% of world’s surface freshwater. In addition to numerous streams, rivers, lakes (including pothole and kettle lakes), springs, spring ponds, and wetlands, over 35,000 islands are found within the Great lakes. There are also unique freshwater features,  such as Manitoulin Island, the largest freshwater island in the world; St. Clair River Delta, the largest freshwater river delta in the world; and the most sand dunes of freshwater origin in the world (TNC 2000).  

The extensive interior wetlands and sand dune systems, such as Lake Ontario’s Presqu’ile, Lake Erie’s Long Point, Rondeau, and Point Pelee, support unique plant communities on large sand pits. Some of these wetlands are also recognized internationally for their outstanding biological significance, including Long Point and Point Pelee on the north shore of Lake Erie, and the National Wildlife Area on Lake St. Clair. Long Point is designated a UNESCO Biosphere Reserve.

Terrestrial Habitats:

The northwestern part of the ecoregion is dominated by mixed forest characterized by white and black spruce (Picea mariana), balsam fir (Abies balsamea), jack pine (Pinus banksiana), trembling aspen (Populus tremuloides), and paper birch (Betula papyrifera). Here, forest fires are an important natural disturbance (ESWG 1995). To the south deciduous forest dominates, with species  such as sugar maple (Acer saccharum), red maple (Acer rubrum), American beech (Fagus grandifolia), hop hornbeam (Ostrya virginiana), basswood (Tilia americana), yellow birch (Betula alleghaniensis), and eastern hemlock (Tsuga canadensis). In the eastern edge of the ecoregion rare alvar communities support prairie species that are at their eastern extremity, and are globally endangered. Ancient eastern white cedars on the limestone cliffs of the Niagara Escarpment have been aged at 700 to 800 years, making them some of the oldest in eastern North America (Ricketts et al. 1999).

Fish Fauna:

From a biogeographic perspective this ecoregion is quite young (Underhill 1986). During the last glacial retreat, fish fauna colonized the Great Lakes from neighboring drainages, including the Upper Mississippi Basin, Hudson Bay, Ohio River valley, and Atlantic coast (TNC 2000). The proximity and multiple connections to these refugia, as well as a relatively moderate climate and diversity of habitats (from small headwater streams to wetlands and deep offshore areas of large lakes) resulted in the ecoregion’s rich diversity of fishes, despite the relatively few endemics. It does, however, contain unique forms of widely distributed species. This region’s freshwater species, and particularly its fish, tend to be adapted to one of two habitat types: lacustrine (lake) or lotic (river and stream) (Underhill 1986). Minnows (Cyprinidae) represent the most diverse fish family in this ecoregion, followed by the salmons, trouts and whitefishes (Salmonidae), perches (Percidae), sunfishes (Centrarchidae), suckers (Catostomidae), and bullhead catfishes (Ictaluridae).

Description of endemic fishes:

An endemic cisco species flock consisting of bloater (Coregonus hoyi), blackfin cisco (C. nigripinnis), deepwater cisco (C. johannae), and shortnose cisco (C. reighardi) has been described in the Great Lakes. All of these species are extirpated in one or more of the Great Lakes in which they originally occurred, and the deepwater and shortnose ciscoes are considered to be extinct. All of these species are thought to have evolved from a common ancestor, lake cisco (C. artedi), within the Great Lakes since their most recent formation c. 14,000 years ago. Siskiwit lake cisco (Coregonus bartlettii) and Ives lake cisco (Coregonus hubbsi) are two other endemics, although experts disagree whether they are separate species from C. artedi. A subspecies of walleye (Sander vitreus vitreus) known as the blue pike (Sander vitreus glaucus) was once endemic to lakes Erie and Ontario, but is now considered extinct.

Other noteworthy fishes:

Many of the over 150 native fish species in the Great Lakes ecoregion are considered to be at risk. Habitat alteration, invasive species, and overexploitation are considered to be the greatest threats to fishes in the Great Lakes Basin. In addition to the endemic fishes listed above, notable fish species at risk in this ecoregion include the extirpated Atlantic salmon (Salmo salar), American eel (Anguilla rostrata), which is virtually extirpated, and the lake sturgeon (Acipenser fulvescens), which has exhibited a precipitous decline (>95% population decline) since the late 18th century. In addition to the many native species at risk, many introduced species have become established in the Great Lakes Basin, including common carp (Cyprinus carpio), goldfish (Carassius auratus), brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), Pacific salmons (Oncorhynchus spp.), sea lamprey (Petromyzon marinus), rainbow smelt (Osmerus mordax), alewife (Alosa pseudoharengus), ruffe (Gymnocephalus cernuus), and round goby (Neogobius melanostomus). Many of these species have had substantial negative impacts on the ecosystems of the Great Lakes Basin.

Other noteworthy aquatic biotic elements:

The Great Lakes ecoregion contains a unique assemblage of aquatic insects, mussels, and planktonic species with both freshwater and marine origins. This has resulted from both glacial advancements, which brought arctic marine and brackish water invertebrates that adapted to the freshwater environment, as well as new freshwater species that colonized the region from other drainages as glaciers receded (TNC 2000).

Many of the mussels are endangered as a result of habitat alteration and invasive species, and many aquatic invertebrate species have been introduced into this ecoregion, largely through ballast water release. These species include the spiny water flea (Bythotrephes longimanus), fishhook water flea (Cercopagis penoi), and zebra mussel (Dreissena polymorpha). These species have also had substantial negative impacts on the ecosystems of the Great Lakes Basin.

Ecological phenomena:

Historically, the lake sturgeon and American eel undertook long spawning migrations, and the lake cisco and lake whitefish (Coregonus clupeaformis) likely formed large spawning schools in the larger lakes. The wetlands of the lower Great Lakes as well as Lake Superior and Lake Huron are crucial for migrating birds and serve as stopovers and major breeding areas.

Evolutionary phenomena:

Morphological radiation related to depth and prey has been identified in lake trout (Salvelinus namaycush) in some of the Great Lakes. Many fish species exhibit morphological variation across this ecoregion as the result of populations being isolated following the last Ice Age and, subsequently, adapting to local environments.

Justification for delineation:

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995). The boundaries were then modified based on the faunal similarity of 166 major watersheds based on a cluster analysis of freshwater fish occurrences in these watersheds. The Laurentian Great Lakes ecoregion includes the watersheds that drain into the Great Lakes and the Great Lakes themselves. This ecoregion has the greatest fish species richness of any ecoregion in Canada. This is a result of proximity and multiple connections to the Mississippian and Atlantic Coastal refugia, relatively moderate climate, and diversity of habitats.

Level of taxonomic exploration:



Abell, R., Olson, D., et al. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.

Eswg (1995) "A national ecological framework for Canada". Ottawa/Hull, Ontario, Canada. Agriculture and Agri-food Canada, Research Branch, Centre for Land and Biological Resources Research; and Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch..

Hubbs, C. L.,Lagler, K. F. (2004). "Fishes of the Great Lakes region" Revised. Ann Arbor, MI: The University of Michigan Press.

Koelz, W. (1929). "Coregonid fishes of the Great Lakes" Bulletin of the United States Bureau of Fisheries 43 297-643.

Mandrak, N. E.,Crossman, E. J. (1992). "A checklist of Ontario freshwater fishes annotated with distribution maps" Toronto, ON: Royal Ontario Museum Misc. Life Sci. Publ..

Maxwell, J. R., Edwards, C. J., et al. (1995) "A hierarchical framework of aquatic ecological units in North America (Nearctic Zone)". St. Paul, MN. North Central Forest Experiment Station, USDA Forest Service.

McNab, W. H.,Avers, P. E. (1994) "Ecological subregions of the United States". U.S. Forest Service, ECOMAP Team, WO-WSA-5. Online.

Ricketts, Taylor H. Dinerstein Eric Olson David M. Loucks Colby J. (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.

Scott, W. B.,Crossman, E. J. (1998). "Freshwater fishes of Canada" Fisheries Research Board of Canada Bulletin 184 966 + xvii..

The Nature Conservancy, Great Lakes Program (2000) "Toward a New Conservation Vision for the Great Lakes Region: A Second Iteration". Chicago, IL.

The Nature Conservancy World Wildlife Fund
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