North America holds roughly one quarter of the world’s fresh surface water with the vast majority concentrated in a handful of enormous natural lakes, according to estimates cited from the U.S. Environmental Protection Agency (EPA).
The Great Lakes alone account for about 21% of the world’s fresh surface water and approximately 84% of North America’s supply. When Canada’s massive northern lakes, including Great Bear Lake and Great Slave Lake, are included North America’s share rises to around 25%.
The estimate refers specifically to liquid freshwater found at the Earth’s surface, including lakes and rivers. Groundwater and frozen water such as glaciers and ice caps are counted separately and represent an even larger share of the planet’s total freshwater.
The Great Lakes contain about 5,439 cubic miles (22,684 cubic kilometres) of water, based on EPA estimates. Compared with an estimated global fresh surface water volume of about 25,600 cubic miles (106,707 cubic kilometres) the Great Lakes account for approximately 21.3%.
Lake Superior alone contains about 2,900 cubic miles (12,100 cubic kilometres) of water. It holds more than half of the total water stored in the Great Lakes and roughly 11% of the world’s estimated fresh surface water.
Lake Michigan contains about 1,180 cubic miles (4,920 cubic kilometres), equivalent to approximately 4.6% of the global fresh surface water supply. Lake Huron holds around 850 cubic miles, while Lake Ontario contains approximately 393 cubic miles and Lake Erie about 116 cubic miles.
Canada’s northern lakes provide another major portion of North America’s freshwater wealth. Great Bear Lake in Canada’s Northwest Territories contains roughly 536 cubic miles (2,236 cubic kilometres) of water, representing about 2.1% of the estimated global fresh surface water volume. Great Slave Lake contains approximately 379 cubic miles (1,580 cubic kilometres), although estimates vary depending on measurements and bathymetric data.
Lake Winnipeg in Manitoba is another significant freshwater body containing around 68 cubic miles (284 cubic kilometres) of water.
Canada also has an enormous number of smaller lakes. Its national climate assessment reports more than 875,000 lakes larger than 0.1 square kilometres, with lakes covering nearly 9% of the country.
Despite their size reservoirs contribute comparatively little to the global freshwater total. Lake Mead, one of North America’s largest reservoirs, has a traditional full-pool capacity of about 28.9 million acre-feet, equivalent to approximately 8.6 cubic miles (36 cubic kilometres). That is only around 0.03% of the estimated global fresh surface water supply.
The Great Lakes contain more than 600 times the full capacity of Lake Mead highlighting the enormous role played by natural lake systems in North America’s freshwater reserves.
Rivers, meanwhile, hold only a small amount of freshwater at any given moment. The U.S. Geological Survey estimates that all rivers worldwide contain approximately 510 cubic miles (2,120 cubic kilometres) of water at a time. Although rivers such as the Mississippi and Mackenzie transport huge quantities of water each year, their standing volumes are relatively small compared with those of the continent’s major lakes.
The one quarter estimate does not include groundwater. USGS estimates that the world contains about 2.526 million cubic miles (10.53 million cubic kilometres) of fresh groundwater. This underground reserve is roughly 100 times larger than the amount of freshwater held in the world’s lakes.
Frozen water is also excluded from the calculation. Glaciers, ice caps and permanent snow contain an estimated 5.773 million cubic miles (24.064 million cubic kilometres) of freshwater worldwide, accounting for nearly 69% of Earth’s freshwater.
Overall, North America’s roughly one quarter share of the world’s liquid fresh surface water is largely driven by the Great Lakes and Canada’s vast northern lake systems. The figures underline the continent’s importance as one of the planet’s major freshwater reservoirs, while also showing that most of Earth’s freshwater exists underground or in frozen form.