6 quadrillion gallons of fresh water; one-fifth of the world's fresh surface water (only the polar ice caps and Lake Baikal in Siberia contain more); 95 percent of the U.S. supply; 84 percent of the surface water supply in North America. Spread evenly across the continental U.S., the Great Lakes would submerge the country under about 9.5 feet of water.
More than 94,000 square miles/244,000 square kilometres of water (larger than the states of New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont, and New Hampshire combined, or about 23 percent of the province of Ontario). About 295,000 square miles/767,000 square kilometres in the watershed (the area where all the rivers and streams drain into the lakes).
United States and Canada -- 10,900 mi/17,549 km (including connecting channels, mainland and islands). The Great Lakes shoreline is equal to almost 44 percent of the circumference of the earth, and Michigan's Great Lakes coast totals 3,288 mi/5,294 km, more coastline than any state but Alaska.
References: Great Lakes Basin brochure, 1990, Michigan Sea Grant
Great Lakes Atlas U.S. Environmental Protection Agency (EPA) This Environmental Atlas and Resource Book is an excellent resource on the Great Lakes, including physical characteristics, natural processes, people, concerns, joint management and new directions (mirrored on Environment Canada's site).