- Only freshwater will sustain human life.
- About 97% of the water on earth is salt water.
- Of the remaining fraction of approximately 3% that is freshwater, over 98% is locked in ice caps, glaciers and groundwater.
- Of the remaining fraction of about 1.2% of all freshwater, about .25% is found at the surface in lakes and streams.
- The Great Lakes contain almost 20% of that .25% – one-fifth of all available surface freshwater in the world.
Great Lakes Volume and Transit Facts
- The Great Lakes contain 95% of the surface water volume of the United States.
- The Great Lakes contain 84% of the surface water volume of North America.
- Only 1% of the volume of the Great Lakes is renewed annually from precipitation and runoff; the water balance of the Lakes is delicate.
- The average drop of water takes 173 years to pass through Lake Superior.
- The average drop of water takes 204 years to pass from Lake Superior to the ocean.
- Spread evenly across the 48 contiguous states, the Great Lakes would turn the U.S. into a swimming pool 9.5 feet deep.
- There are approximately 35,000 islands in the Great Lakes, including the largest lake island in the world, Manitoulin.
- There are about 10,900 miles of Great Lakes shoreline, 200 miles less than the distance between Detroit and Perth, Australia.
- Measured by surface area, Lake Superior is the largest freshwater lake in the world, Lake Huron is third, Lake Michigan is fourth, Lake Erie is tenth and Lake Ontario is twelfth.
- Lake Superior could contain all the other Great Lakes plus three more lakes the size of Lake Erie
This list is just one idea; experts can and do have their own lists, many based on extensive grounding in science and/or environmental education.
You will find slightly different figures in different sources, demonstrating the inexactness of much of our knowledge about the Great Lakes. The Great Lakes Information Network (https://www.glc.org/lakes/) pegs the total at about one-fifth, US EPA (https://www.epa.gov/greatlakes/great-lakes-facts-and-figures) at about 21%, and Environment and Climate Change Canada (https://www.ec.gc.ca/grandslacs-greatlakes/default.asp?lang=En&n=3F5214D0-1) says it’s 18%.