Dams and Diversions

Overall, Canada is blessed with abundant freshwater resources, but their availability varies considerably from one season or year to another, and from one region to another.

Manic 2
Hydro-Québec's Manic 2 is the largest hollow-joint gravity dam in the world (Corel Professional Photos).

Dams and Diversions

The principal means of regulating stream flows and Lake levels. Dams are barriers constructed across watercourses to impound flows; diversions convey water from many of the resulting impoundments or Reservoirs by means of Canals, ditches or pipelines for use elsewhere in the same or in other drainage basins.


Overall, Canada is blessed with abundant freshwater resources, but their availability varies considerably from one season or year to another, and from one region to another. Faced with Floods, Droughts and other problems of water supply, engineers have been engaged for some time in constructing projects which, in effect, redistribute nature's regime to suit the temporal and spatial demands of a growing economy.

Dams and diversions serve a wide range of Water needs in Canada, including provision of water supplies for Irrigation, power generation, flood protection, maintenance of navigation levels and recreation, municipal and industrial uses.

Settling Canada

In the colonial period, settlers of Upper and Lower Canada impounded small streams to power their grist and sawmills, sometimes also to float logs to market. Navigation on larger watercourses often required canals and locks such as the Royal Engineers provided to maintain depths and bypass rapids on the St Lawrence, Ottawa and Rideau rivers. Gradually projects increased in number and size as the new Dominion expanded westward.

Shortly after the turn of the 20th century, irrigation projects were taking shape on the dry Prairies; communities such as Winnipeg and Victoria sought to secure water supplies for their future growth; and hydroelectric power generation was already becoming a new industrial panacea throughout the country.

Era of Project Building

In retrospect, it was not until the mid-20th century that water resources development reached a level that launched the great dam and diversion building era in Canadian history, roughly 1950-90. Large-scale exploitation of Canadian waterways began in earnest in the early 1950s with such projects as Alcan's Kemano diversion in central BC to power its Kitimat aluminum smelter, the St Mary Irrigation Project (Alberta) and the international St Lawrence Seaway and Power Project. It continued in the 1960s with the Columbia River Treaty and Peace River power projects (BC); the multipurpose Gardiner Dam (Saskatchewan); the Winnipeg Floodway and first Nelson River hydro projects (Manitoba); the Manicouagan-Outardes development (Québec); and the Churchill Falls project (Labrador).

In the 1970s the Lake Winnipeg and Churchill-Nelson rivers project (Manitoba) and the James Bay Project (Québec) initiated a scale of interbasin diversion unprecedented on the continent. The pace of construction began to slow in the 1980s, however, with only Québec continuing at a high level of activity in order to complete the La Grande (James Bay I) project.

Elsewhere, projects struggled through controversy to completion (Rafferty-Alameda, Sask; Oldman River, Alta) or were shelved indefinitely (Kemano II, BC; Conawapa River, Man; Moose River redevelopment, Ont; Lower Churchill River dams, Labrador). The era of major dams and diversions appears to have drawn to a close in Canada, notwithstanding optimistic predictions expressed in the late 1980s about Canadian water and hydropower exports to the US under freer trade arrangements.

Changing Priorities

A combination of physical, economic, environmental and social factors is responsible for the declining popularity of major water storage and diversion projects. The best sites on the most accessible drainage systems have already been developed. Demand for more water and Energy has slowed in an economy in recession and searching for efficiencies in use as a less costly alternative. Public unrest has also increased, with more cases documented of megaproject impacts on environmental processes and on those communities which have been displaced or otherwise disadvantaged.

Distribution of Projects

Canada has so much natural storage of water in lakes that artificial storage gained by creating new reservoirs or enlarging existing lakes remains small by comparison; but it has grown to cover an area about the size of Lake Ontario.

Canada now ranks as one of the world's 10 leading dam builders. Aside from many thousands of unrecorded smaller dams, the most recent Register of Dams in Canada records 800 large dams in the late 1990s. The largest number are in Québec, followed by BC, Newfoundland and Ontario. The total flow of water diverted between drainage basins in Canada is enormous - 4450 m3 per sec. If all this flow were combined to form a new river, it would be Canada's third largest, after the St Lawrence and Mackenzie.

No other country diverts nearly as much water. Of the 54 projects identified, the most recent are also the largest: La Grande (James Bay Island) project (Québec), Churchill-Nelson diversion (Manitoba) and the Churchill Falls project (Labrador); 3 projects incorporating 7 diversions make up two-thirds of all water diverted within Canada. Again, Québec dominates the geographical pattern.

Purpose of Projects

The overwhelming majority of Canada's dams and diversions have been built to serve hydroelectric power generation. Irrigation (especially southern Alberta), flood control (Manitoba) and municipal supply projects (Regina, Winnipeg and London) assume importance regionally or locally. There is no doubt Canada is "hydro country," with 95% of the volume of water stored behind large dams and diverted between basins serving a hydroelectric function.

This is quite a different pattern than found in most other countries where waterways are dammed and diverted for consumption of water on the farm or in the city. In Canada it is electricity, not water, that is transported to market from such projects.

Project Impacts

The principal benefits from water projects are normally recorded in statistics on electricity production, irrigated crops, water-borne commerce, flood damage reduction and municipal, industrial and recreational water use services. Not as easily quantified are wide-ranging and long-term ecological and social consequences.

Creation or enlargement of reservoirs displaces people, disrupts wildlife habitat and can have some impact on local climate and geological stability. Evaporation is increased from a reservoir's expanded surface area and sediment is trapped in its slow-moving waters, resulting in both flow and nutrient-bearing silt reductions downstream.

One of the most serious problems discovered in investigating the consequences of enlarging Southern Indian Lake to serve as a reservoir for the Churchill River diversion was the conversion of Mercury in flooded soils and vegetation to toxic methylmercury that accumulated in fish, making them unsafe for human consumption for years to come. Other problems experienced for the native fishery there were the turbidity caused by slumping of lakeshore materials as permafrost melted in the rising waters, and the cutoff of whitefish migration downstream by the dam at the lake outlet. Much of the native community itself had to be relocated because of the flooding of their shoreline location.

Other problems are experienced downstream, as flow patterns change below reservoirs and points of diversion. Hydro projects upset the natural pattern of flooding, releasing more water during winter to suit energy demands, and much less during spring, when biological needs are reawakening in wetlands, deltas and estuaries.

Another area of concern is the riparian forest habitat of drier prairie floodplains, which is having difficulty maintaining appropriate moisture conditions for regeneration below storage and diversion locations. Interbasin diversion of water also occasionally runs the risk of transferring undesirable fish and associated parasites, bacteria and viruses into drainage systems unprepared to resist them; that is why Canada continues to oppose certain canal and pipeline routes of the Garrison diversion project in North Dakota.


Like our national symbol, the beaver, we Canadians have dammed one waterway after another, and diverted many of them beyond their natural boundaries, while establishing our dominion across the northern half of this continent. We have also experienced mixed results from these practices, leading to a reconsideration of the merits of further changes to nature's regime.

There are still large unknowns surrounding the future of dams and diversions in this country. The operation of some existing projects may be changed to mitigate undesirable effects on certain interests. There remains also the disturbing possibility of increasing demands for water as a result of Global Warming and pressures to divert water south of the border.

See alsoWater-Borne Diseases.