The Great Lakes are one of the world's greatest reserviors of fresh water, the foundation of Ontario's economic development, a primary force in ecological systems, and a base for pleasure and recreation. These lakes and their relationship with people of Canada and the United States can be useful as a subject for teaching the impact of human activity on freshwater ecosystems. This issue of "Seasons" is devoted to the topic of the Great Lakes. Articles included address: (1) the geologic history of the region; (2) the ecology of the region; (3) shoreline ecology; (4) the status of the pollution situation in the lakes in 1989; (5) pollution threats to human activity; (6) organizations devoted to protecting the lakes and associated areas; and (7) how humans cope with the environment surrounding the lakes. A directory of organizations can be found at the end. (CW)