Lakes and Rivers

Aerial view of lakes in Northern OntarioOntario’s lakes and rivers play a vital role in sustaining Ontario’s economy and the quality of life of Canadians. They provide us with water for a number of goods and services including drinking water, irrigation and industrial processes, food and recreation.


There are approximately 250,000 lakes in Ontario. These lakes, including the Great Lakes, have a total surface area of 181,153 sq. km. (69,944 sq. mi.) which is about 17% of the total area of the province. This is considerably higher than the national percentage of 8%.

Lakes are defined as large bodies of inland water.  If surface water flows to a place that is surrounded by higher land on all sides, a lake will form. If a dam is built to hinder a river's flow, the lake that forms is a reservoir.


Lakes are an essential source of water in Ontario.  The Great Lakes hold about 1/5 of the world's fresh surface water supply.  Most of our drinking water, as well as water used for irrigation, industry, and hydropower, come from freshwater lakes and reservoirs. 



A river is a natural waterway that moves water over the land from higher to lower elevations. It is an integral component of the water cycle. The water within a river comes from surface runoff from precipitation, from groundwater and from the release of water in stored reservoirs.
Southern Ontario's rivers flow into the Atlantic Ocean by way of the Great Lakes and the St. Lawrence River system. Most northern Ontario rivers empty into James Bay and Hudson Bay.


The Importance of Lakes and Rivers:


Lakes and rivers are vital components of our environment as they:

  • are an important source of freshwater.
  • help replenish groundwater supplies.
  • provide habitat for numerous species of plants and animals
    including species at risk.
  • can help ease impacts of floods by storing large amounts of water and droughts by releasing water during shortages.
  • are essential components of the water cycle.
  • moderate local climate by absorbing heat in hot weather and releasing heat in cool weather
  • are an important source of renewable energy

Related Links

The longest river in Ontario is the Albany River which is 980 km long and has a drainage basin of 134 000 km2