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Moses-Saunders hydro dam, St. Lawrence River, Ontario


The health of Canada’s environment is intimately linked to our vast network of rivers, lakes and wetlands. They provide critical habitat and serve as travel routes for innumerable species of wildlife. It is immensely important that the ecological integrity of aquatic ecosystems is maintained.

Unfortunately, aquatic ecosystems and their wildlife face many threats in Canada. These include industrial, agricultural and residential pollution, wetland destruction, and deforestation of adjacent and nearby uplands. One of the most serious threats is posed by hydroelectric and other types of dams that physically obstruct waterways, fragment or destroy aquatic habitat, block fish migration, and alter water flow regimes. In some cases large volumes of water are diverted from one watershed to another. Dams in Canada are seldom constructed with fish passageways, effectively blocking fish from travelling upstream to critical spawning sites. On the way downstream, hydro turbines are a more source of injury and mortality. As a result many species have been devastated, especially in southern Canada. Salmon have declined drastically on both Canada’s east and west coasts and been extirpated from Lake Ontario and its tributaries. The American Eel has been eliminated from much of its historical range in Ontario. Lake Sturgeon have suffered steep declines throughout much of their range.

Below we briefly discuss the effects of hydroelectric development on the environment.

Hydroelectricity – not green or clean

Hydroelectric development is often touted as a source of “green” and “clean” energy by government and hydro developers. Unfortunately this is not the case, as hydro has a major negative effect on aquatic ecosystems and wildlife, and on water quality. This applies to both large and small developments. Large developments typically have a large environmental footprint and can involve ecosystem destruction at a massive scale. Small developments typically produce only small amounts of power. Therefore, to produce a large amount of power numerous sites must be developed, with cumulative impacts that can be severe.

Some of the negative effects of hydro development are listed below.

Environmental effects of hydroelectric development

  1. Loss of most productive habitats by flooding of river valleys, lakes and wetlands upstream of the dam and generating station. Reservoirs are typically created to store water for hydro facilities. They may extend upriver from the generating station or be located far upstream. They flood low lying areas such as wetlands, the shorelines of lakes and river banks. These areas, which typically have high biodiversity, are permanently lost and wildlife drown. In some cases prime farmlands, which are often located in river valleys are flooded and farmers or communities displaced.


  2. Loss of forest habitat at greater elevations. Reservoirs often flood substantial areas of forested lands well away from the river itself.


  3. Interruption of a river’s natural flow cycle. Aquatic wildlife and vegetation are adapted to and often rely on the natural flow of a river and its seasonal variation. Hydro development disrupts that pattern both in the reservoir(s) above a dam and in the river below the dam.


  5. Changes in water temperature. Changes in water temperature due to hydro development can have significant negative effects on some species.


  6. Damage or destruction of delta/estuary habitats far downstream of the generating station. Deltas and estuaries are among the most productive habitats on earth. The health of these ecosystems and their wildlife rely on natural seasonal flooding regimes and on sediments transported by the river. Hydro facilities, often far up the river can have devastating effects by eliminating the natural flooding cycle, and decreasing sediments. The Peace River delta, one of the continent’s most significant wetlands, has been severely damaged by the construction of two upstream hydro facilities.

  7. Sedimentation. Sediments that normally are flushed downstream are deposited in slow moving waters of hydro reservoirs. They no longer provide nutrients downstream. The sediment build-up behind the dam can cause nutrient loading and a decrease in oxygen.

  8. Effects of peaking operations. In peaking operations water is released from the reservoir above the dam when demand for electricity is high, but held back when demand is low such as at night or on weekends. Thus the water flow can change dramatically over a short period of time and have significant negative effects downstream. In particular, the release of large quantities water  can cause severe damage to downstream riverbanks and their habitat. In addition fluctuations in reservoir water levels can render the shorelines of the reservoir unstable.

  9.  Damage or destruction of ecological links. Rivers form important ecological links between natural areas which may be damaged or severed by hydro development.

  10. Fragmentation of a river’s ecosystem and the blocking of fish migration routes. Dams act as a physical barrier that fragments a river’s ecosystem and isolates aquatic species that live upstream or downstream. In particular, hydro dams usually disrupt or eliminate fish migration. Fish ladders are almost never installed. Therefore fish are unable to move upstream past the dam. On the way downstream fish are killed and maimed in the turbines. This has had drastic effects on many fish populations across Canada.

  11. Dewatering sections of the river. In some instances a large portion of a river’s flow is diverted via a pipe or channel to the generating station and then back to the river. In extreme cases this can leave a section of the riverbed essentially dry. In other cases a river may actually be diverted into another watershed to feed generating stations there. This has occurred for example in northern Manitoba where the Churchill River has been diverted into the Nelson River.

  12. Greenhouse gas emissions. Decaying vegetation in hydro reservoirs causes the release of the greenhouse gases methane and carbon dioxide. Flooded peatlands are thought to be the largest emitters associated with reservoirs in the boreal forest region. Flooded peatlands and forests no longer sequester carbon. In addition, substantial greenhouse emissions are associated with the production of the materials for the dam and with the operation of machinery during construction.

  13. Mercury pollution. Bacteria in reservoirs convert inorganic mercury in flooded soils to methyl mercury which is then concentrated up the food chain. Mercury is a strong neurotoxin and when contaminated fish are consumed by humans they can suffer very serious health effects. High levels of mercury have been reported in fish from many Canadian hydro reservoirs and have resulted in bans or restrictions on the human consumption of fish.

  14. Power corridors and access roads fragment wilderness and natural habitat. Power corridors and access roads may extend for long distances through what were previously wilderness areas depending on the remoteness of the location of the generating station.

  15. Service roads allow access for poachers and other illegitimate users.

  16. Service roads and power corridors act as conduits for invasive species. Invasive species pose a threat to many ecosystems across the country.

  17. Interbasin water transfers associated with some hydro developments can permit the movement of invasive species from one basin to another.

  18. Cumulative effects of multiple hydro projects in a single watershed. Environmental Assessments seldom consider the cumulative effects of the various existing or proposed hydro projects on the river, nor the effects of dams constructed for other purposes. The cumulative effects of several smaller dams can often equal that of a single large dam.

Other effects of hydro development

Hydro development has other major drawbacks that are not necessarily of an environmental nature.

  1. Damage to recreational resources and ecotourism. Many recreational and scenic resources, such as canoe routes, scenic waterfalls and rapids occur along rivers and can be lost due to hydro development. This has a direct negative impact on ecotourism.

  2. Destruction of historical, archeological and cultural sites. Typically historical, archaeological and cultural sites are clustered along river banks and lake shores, as these were the places that First Nations and European settlers chose for their settlements and camps. Rivers formed the main transportation routes across much of the country prior to 1900, and in the north until the mid 1900's. Portages around waterfalls and rapids are particularly rich sites. Unfortunately they are also the sites of hydro generating stations and associated infrastructure. Many important sites have been permanently lost due to hydro development. Many more are threatened.

  3. Safety concerns. Hydro dams are a safety hazard for downstream users such as boaters and swimmers, because of the large fluctuations and flows that occur downstream. In addition, catastrophic dam failures due to earthquakes or aging facilities can cause substantial damage and loss of life.


Examples of hydroelectric proposals

Two examples of a myriad of hydro project proposals that threaten Canada’s rivers, aquatic ecosystems and wildlife are outlined below.


Peace River Site C hydroelectric proposal, northeastern British Columbia

Site C, a mega hydroelectric project is planned for the Peace River in northeastern British Columbia. The proposed dam would create a reservoir stretching more than a hundred kilometres (LINK) along the river and its tributaries. It would flood critical wildlife habitat, prime farmland, and historical and First Nations cultural sites. It will likely have detrimental effects on the Peace River delta, a United Nations World Heritage Site downstream.

Wildlife habitat: The section of the Peace to be flooded forms a critical ecological link in the south to north Yellowstone to Yukon (Y2Y) Conservation Initiative.  Hydro development threatens to sever this link for species such as the grizzly bear. The Peace River Valley provides the only breach in the Rocky Mountains and hence is an important east-west corridor for wildlife. Wildlife have already been drastically affected by development along the Peace, especially by the WAC Bennett dam and its huge reservoir which were constructed farther upstream in the 1960’s.

Peace River delta: The Peace River delta is a huge freshwater delta located downstream in Alberta where the Peace River meets the Athabasca-Slave River system at the west end of Lake Athabasca. It is of international importance and has been designated a United Nations World Heritage Site. The wetlands of the delta have already been significantly affected by the WAC Bennett dam because of alteration of the river’s natural flow regime. No environmental assessment was carried out when that dam was constructed in the 60’s. It is unclear how serious the effects of the new proposed project will be for the delta as the necessary environmental studies have not been conducted.

Farmland: Only a tiny fraction of British Columbia is suitable for agriculture. Much of the Province’s food is imported. One would have thought that the protection of the Province’s prime farm land would be a top priority. Think again! The portion of the Peace River Valley that would be lost due to flooding by the Site C dam includes a large area of class 1 and class 2 farmland, which is considered the best in northeastern BC.

There is fierce opposition to the Site C project from environmentalists, farmers, and First Nations.

In October 2014, a federal-provincial Joint Review Panel granted environmental assessment approval of the project.

In November 2014, local First Nations filed a law suit to stop the project due to the devastating effects which it would have on their traditional lands. Alberta First Nations filed a separate lawsuit claiming that the downstream effects of the project on the Peace River Delta have not be properly considered.

In December 2014, the BC government approved the project.

In May 2015, Heritage Canada National Trust designated the Peace River as one of Canada's 10 Most Endangered Places because the Site C project will destroy many First Nations traditional and sacred sites, other historical sites, wildlife habitat and prime farmland.

The site C project, which was first developed nearly half a century ago, and has been rejected in the past, must be rejected once again.

For more information:

Stop Site C

Wilderness Committee (includes a map of the portion of the Peace River that is affected)

Peace Valley Environmental Association

Report on Peace River Valley natural and cultural values

Y2Y Conservation Initiative

Its Our Valley


Namakan River High Falls hydroelectric proposal, northwestern Ontario

The Namakan River flows through the heart of the Quetico-Superior wilderness which straddles the border between northwestern Ontario and northern Minnesota. It is the last large free-flowing river in the region and forms an ecological link between three protected wilderness parks, Quetico Provincial Park in Ontario and Voyageurs National Park and the Boundary Waters Canoe Area Wilderness in Minnesota.

Namakan River in the heart of the Quetico-Superior Wilderness

The Namakan is home a healthy population Lake Sturgeon, a species that is listed as endangered in northwestern Ontario. The river is a critically important natural laboratory for the study of Lake Sturgeon and other species because it has not been altered by hydro development. Detailed acoustic telemetry studies have been carried out and demonstrate that Lake Sturgeon migrate along the length of the river from Namakan Lake to Quetico Park. The Namakan is also the only known location in Ontario of the endangered Pygmy Snaketail dragonfly, which is known to survive only in free-flowing rivers. The Quetico-Superior region is known internationally for its network of wilderness canoe routes. The Namakan is an important element of that network and has been used by First Nations for millennia as well as forming a link in the fur trade canoe route from the Great Lakes to western Canada in the 1700’s and 1800’s.

Over the past several years proposals have been made to develop up to three hydro generating stations along the Namakan at Myrtle Falls, High Falls and Hay Rapids. The most serious current proposal is centred on High Falls. It would create a reservoir up to and along the boundary of Quetico Park.

Namakan River, Ontario

It is critical that the Namakan hydro projects be rejected and that the Ontario government permanently remove the sites along the river from consideration for future hydro development. The reasons are many:
  1. The threat to the ecological integrity of the three nearby wilderness parks.

  2. The threat to the ecological link between the parks.

  3. The threat to Lake Sturgeon, an endangered species, and their migration route along the river.

  4. The threat to the river’s use as a natural scientific laboratory for the study of Lake Sturgeon and other species.

  5. The threat that a dam would extirpate the endangered Pygmy Snaketail from Ontario as its only known location is on the Namakan.

  6. The threat to the wilderness character of the region and it internationally-known canoe route network.

  7. The threat to the historical, archaeological and First Nations cultural sites along the river.

In future it is important that pristine sites on waterways not be opened to development proposal until after there has been a study with public input into the site's suitability. Sites within or adjacent to protected areas, sites within sensitive ecosystems, and important historical or cultural sites should be automatically rejected. Sites that are opened to development proposals should then undergo thorough environmental and archaeological assessments carried out by an independent agency, not the project proponent.

For more information on the Namakan:

Voyageurs National Park Association

Peaceful Parks Coalition

Ministry of Natural Resources report on Sturgeon migration along the Namakan

For information on other rivers at risk in Ontario:

Ontario Rivers Alliance

For information on the many negative environmental effects of hydroelectric development, both large and small:

Ontario Rivers Alliance, Hydro Impacts 101 Report