In the heart of North America lies a vast chain of inland seas whose depths contain more than one-fifth of the surface freshwater on the planet, the largest natural reservoir on an ever more thirsty Earth. We call these freshwater seas the Great Lakes. The five connected bodies, which together form America's fourth coast, have played a fundamental role in the history of North America and – because their resources-rich basin became the heartland of American industrial might – the history of the world as well. The region’s ecosystem contains more than 3,500 species of plants and animals, including some that are found nowhere else in the world, and its economy is one of the most diverse on the continent, home to half of Canada's manufacturing capacity and one-fifth the manufacturing capacity of the United States. For the first time, American television audiences get a close-up, in-depth look at this amazing natural phenomenon in a 2-hour documentary, Freshwater Seas: The Great Lakes, filmed in partnership with Detroit Public Television.