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Lac Saint-Louis et Îles-de-la-Paix (QC134)


Lac Saint-Louis et Îles-de-la-Paix (QC134)

Montréal, Québec

Latitude 45.392°N
Longitude 73.811°W
Altitude 20 - 22m
Area 118.51km²

Site Description

Lac St-Louis is a widening of the St. Lawrence River south of Montreal, Quebec. The site consists of the river itself, the Îles-de-la-Paix National Wildlife Reserve, but excludes all other islands and the mouth of the Beauharaois canal. The lake is mostly shallow (except in the St.Lawrence seaway) with these areas being marshy or colonized by many aquatic grasses. Most marshes are on the south side of the lake, while the grassy areas are on the north side. Most of the shores are urbanized. The Îles de la Paix are relatively flat and marshes occupy the centre of most of them but there are also a few clumps of trees. There are about 15 rare plants in the area.


Lac St-Louis ranked fifth in importance for waterfowl of the St. Lawrence system in studies conducted between 1974 and 1981. Fall peak one-day counts, averaged between 1974 to 1978, tallied 32,230 ducks, a globally significant number. These birds are a mix of dabblers (Mallard, American Black Duck, Blue-winged Teal, American Wigeon, and Northern Pintail), scaup (mainly Greater), Common Goldeneye, and mergansers (mainly Common). Scaup are often present in very large numbers. The 1974 to 1978 one-day peak average for this species was 27,000 birds. Additionally, on one occasion 39,000 scaup were seen southwest of Îles-de-la-Paix. Smaller numbers of ducks are found here in the winter and spring.

Many dabbling ducks nest on Îles-de-la-Paix, including American Black Duck, Mallard, Blue-winged Teal, Northern Pintail, Green-winged Teal, Northern Shoveler, American Wigeon and Wood Duck, although the numbers are not especially high for the region. Thirty to 40 pairs of Double-crested Cormorants nested on Îles-de-la-Paix in 1997 and 1998, although the colony was inactive in 1999. Great Blue Heron nests numbered between 18 and 25 pairs in the late 1990s. Black Terns have also nested on the site although their population has not been monitored.

Conservation Issues

Intensive hunting (15,000 birds per year), shore degradation and development all affect the waterfowl in the lake. Human activities such as kitesurfing around Îles de la Paix and the increasing use of personal watercraft in the Maple Grove area could have detrimental effects on the nesting of water birds. The shores of the IBA are regularly littered with pieces of paper coming from Kruger?s storage site and garbage left by reckless picnickers.

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
Whooping Crane
Number Year Season
Least Bittern
Number Year Season
12 - 192010Summer
Number Year Season
Greater Scaup
Number Year Season