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Barrage de Beauharnois (QC131)


Barrage de Beauharnois (QC131)

Beauharnois, Québec

Latitude 45.320°N
Longitude 73.901°W
Altitude 29 - 49m
Area 5.53km²

Site Description

This site is located two kilometres east of the city of Beauharnois, and 30 km west of Montréal, Québec. Barrage de Beauharnois is situated at the mouth of the Beauharnois Channel and borders Lac Saint-Louis (a widening of the St. Lawrence River). The hydroelectric dam, two locks and a Hydro Québec power station are present on the site. From Beauharnois Channel, the water passes through turbines and emerges into three channels before entering Lac Saint-Louis. Immediately below the dam, a road crosses two islets. These islands and the surrounding waters make up this Important Bird Area.


Thousands of Ring-billed Gulls colonize the islands below the dam from March to December. Throughout the 1990s, an average of 6,742 breeding pairs were present on the island, which is 1% of this species' national population. During this time the lowest count was 5,449 pairs (1994) and the highest was 8,059 pairs (2000). The landowners have installed exclosures on parts of the islands to prevent the gulls from nesting, but the gulls have moved to another part of the site on the other side of the road.

This site is also an important wintering site for gulls. In total, 17 gull species have been seen here. During the winter, gull flocks may contain as many as 25,000 birds. In November and December, Herring Gull flocks and Ring-billed Gull flocks are as large as 15,000 birds. In winter, Great Black-backed Gull, Iceland Gull, and Glaucous Gull are common, and Bonaparte's Gull is the most common small gull. The dead fish coming out of the turbines are a great food source for the gulls.

Hundreds of terns (mostly Black Tern and Common Tern) also frequent the site in spring and fall. Five percent of the national Black Tern population (500 birds in 1984) and close to one percent of the North American Common Tern population has been recorded here. Pomarine Jaeger, Parasitic Jaeger, Laughing Gull, Franklin's Gull, Little Gull, Black-headed Gull, Ivory Gull, Sabine's Gull, Mew Gull, Lesser Black-backed Gull, Thayer's Gull, California Gull, Forster's Tern, Arctic Tern and Caspian Tern are also seen here irregularly.

In addition to the gulls, large numbers of swallows use the site during fall migration. Up to 72,000 Tree Swallows (1976) and 500 Bank Swallows (1977) have been recorded.

During migration, small numbers of ducks and shorebirds use the site, and occasionally Barrow's Goldeneye and Peregrine Falcon (nationally vulnerable) are seen.

Conservation Issues

In the last few years, nets have been installed to limit the number of gulls nesting on the site. Some natural habitats of the IBA, including the adjoining islet, were impacted by the work undertaken around the dam in 2013. This site may be vulnerable to pollution; lake sediments contain elevated concentrations of mercury. Barrage de Beauharnois is inside the Priority Intervention Zone of the Haut-Saint-Laurent, and the area upstream of the power station has been designated a No Hunting Zone. The Beauharnois Canal is part of the Beauharnois-Salaberry Regional Park.

Fish Habitat

A variety of freshwater and diadromous fish coexist in different habitats in the IBA. We found between 70 and 80 species (including historical records) in the area. Several species, such as the northern pike, the yellow perch and the common carp exploit the aquatic vegetation and the floodplains as a spawning ground, a nursery and a feeding ground. Others, such as walleye, freshwater specie with an important economic value in Canada prefer rather to spawn in fast flowing waters. A special feature of this area is the presence of salmonids introduced for sport fishing (brown trout, rainbow tout, and salmons). Salmons were introduced in the Great Lakes and some drift into the St. Lawrence River where they are sometimes caught by anglers. Brown trout and rainbow trout were also stocked in riffles (in the river) for sport fishing.

Several pressures threaten the availability of fish habitats: the creation of embankments, the artificialization of banks, the residential, commercial and industrial development as well as developing the road network, while agricultural, industrial and urban waste deteriorate the water quality. The Eastern sand darter, among others, is very vulnerable to pollution and it is now on the list of endangered species. Among the species listed at risk frequenting the site, we found the lake sturgeon, the channel darter, the bridle shiner, the American eel and some historical records mention the presence of copper redhorse, a fish endemic to Canada designated endangered. In addition, the presence of invasive species such as round goby, threatens the natural dynamics of ecosystems and the water level regulation of the Great Lakes creates risks for the availability of spawning habitats of certain species.

Major species present:
American eel
American shad
Bridle shiner
Brown trout
Channel darter
Common carp
Copper redhorse
Eastern sand darter
Lake sturgeon
Northern pike
Rainbow trout
Smallmouth bass
Yellow perch


The sector is characterized by clear, alkaline and slow flowing water. Theses conditions promote dense plant bed that can cover up to 50% of the water bodies. Submerged plant beds are dominated by wild celery and Eurasian water-milfoil, while emergent marshes are filled with bulrushes, arrowhead and cattails. Several duck species forage in these areas, including the scaup that is fond of wild celery.

Shoreline erosion, whether due to natural factors (wind, freezing and thawing cycles, absence of ice protecting the river banks in spring) or human actions (waves caused by ships), all threaten the riparian habitat. Water level fluctuations affect the ecology of plant and animal species that live there. A significant and prolonged decrease of bank immersion could affect flora by promoting more land species such as shrubs or even trees. In addition, the spread of invasive species exerts considerable pressures on the native flora of these habitats.

Major species present :
American bulrush
Broad-leafed arrowhead
Broad-leafed cattail
Eurasian water-milfoil – invasive species
Great bulrush
Narrow leaf cattail
Sessilefruit arrowhead
Wild celery

IBA Criteria Habitats Land Uses Potential or Ongoing Threats Conservation Status
Herring Gull
Number Year Season
3,000 - 5,0001994Fall
3,000 - 7,5001984Winter
2,500 - 5,0001984Fall
8,000 - 10,0001983Winter
3,000 - 10,0001983Fall
2,500 - 3,5001972Fall
Little Gull
Number Year Season
2 - 71991Fall
Greater Scaup
Number Year Season
Ring-billed Gull
Number Year Season