The Great Lakes are one of the world's greatest reservoirs of fresh water, the foundation of Ontario's economic development, a primary force in ecological systems, and a base for pleasure and recreation. They are also a magnificent resource for the teachers of Ontario. Study of the Great Lakes can bring to life the factors that shape the ecology of Ontario. It can provide a vehicle to demonstrate the economic forces that created Ontario's industrial base. It can illustrate the effects of carelessness and indifference in polluting these vast waters, and the results of cooperative action in combating some of that pollution. This guide is designed to allow teachers to easily make use of Great Lakes topics. Materials in this guide could be used either together or independently. They are arranged in six units: Overview of the Great Lakes; Abiotic Characteristics; Biotic Characteristics; Social and Economic Focus; Under Chemical Siege; and Conserving the Ecosystem. Apart from providing background information, supplementary questions for student review, and suggested group and individual activities, each unit has attitude, skill, and knowledge objectives defined. By permitting a quick assessment of the usefulness of that unit for a particular course, it is hoped these objectives will assist teachers who wish to make use of this material within existing courses. (CW)