Great American lakes belong to the Atlantic Ocean basin because they drain the 1,200km long St. Lawrence River, with an average annual flow of 7,800 m3 / s, which makes an annual 250 km3 and corresponds to the total Volge flow (240km3 per year). All together representing the largest freshwater surface and mass of water on Earth. Their total area is 245,692 km2, which is almost twice the surface of the Adriatic Sea (138,595 km2). The area of the basin is 736,000 km2, of which 59% is on the territory of the United States and 41% in the territory of Canada. The length of the coast line is 15,450km. Of this, the United States holds 8,700km and Canada 6,750km. Europeans first discovered the Great Lakes and the lakes were partially explored by the French in the 17th century. Brul Etina is considered the first white man to see Lake Huron. It was in 1612, when he lived with Huron Indians. He then stayed on Lake Ontario. In 1615, Samuel de Champlain was on the River St. Lawrence, then landed on the Lake Ontario.Physical limnology studies the appearance of lake basins of their shape and relief, the radiation-thermal regime of the lake, evaporation, color and transparency, the movement of lake water and water balance of the lake, flooding of the lake with deposits and their fading. Methods of study and instruments are almost the same as in oceanology. They are mostly used slightly smaller simpler instruments because the lakes are mostly, in relation to the sea and oceans, smaller areas. However, large lakes, such as the Great Lakes in America, are studied by the methods and instruments used in the study of the sea.