The Great Lakes hold about 6 quadrillion gallons of water, making them the largest system of freshwater lakes in the world. Quadrillion is a one followed by 15 zeroes, so that's a lot of water! The Great Lakes contain about 21% of the world's freshwater surface area and 97% of North America's.
These five lakes are huge: Superior, Huron, Michigan, Erie, and Ontario. Together they cover over 94,000 square miles and have an average depth of 279 feet. That's like having a lake the size of Oklahoma filled with almost three times as much water as all 50 states use in a day!
The Great Lakes hold enough water to fill all the reservoirs west of the Mississippi River twice over. In terms of volume, this is equivalent to about 1% of Earth's total freshwater supply. And yet despite their size and importance, the Great Lakes are shockingly vulnerable to depletion and pollution.