Lake Erie's retention time, by contrast, is only 2.6 years. The waters of the Great Lakes are constantly in motion. This movement, which is called the hydrological cycle , is essential for the survival of all life in the Great Lakes Basin. Evaporation Evaporation from the surface of the watershed occurs as water comes into contact with dry, relatively warm air, and forms water vapour. This vapour can remain as a gas or condense in the air to form clouds or fog.
Evaporation is greatest when the differences between air and water temperature are greatest.
The timing of this peak varies by lake. Because the lakes are so large, their surfaces release a great deal of water into the air. The lakes vary a great deal in this respect, however. A shallow, warm lake, like Lake Erie, experiences a great deal more evaporation than a deeper, colder lake, like Lake Superior. Water also evaporates from vegetation, soil, streams, ponds, and smaller lakes.