Ontario has four major regions. They are the Canadian Shield, Hudson Bay Lowland, Great Lakes Lowland, and Saint Lawrence Lowland. The Canadian Shield covers two-thirds of Ontario and is made of igneous and metamorphic rocks that form flat plateaus and low hills. The Hudson Bay Lowland has flat sedimentary rocks. The St. Lawrence Lowland is less than 91 miles high and is part of the sand and clay plains. The major rivers of Ontario are the Severn, Winisk, Attawapiskat, Albany, and Abitibi.
Rivers that drain into the Great Lakes-St. Lawrence drainage basin are the Ottawa, French, Grand, adn Thames Rivers. Many of these rivers are used to produce hydroelectricity.
Ontario has many big lakes. They include Lake Nepigon, Lake of the Woods, Lac Seul, Lake Abitibi, Lake Simcoe, Rainy Lake and Big Trout Lake.