L'Assomption River

The Assomption River (in French Rivière l'Assomption, named after the Assumption of Mary) is the most important waterway in the Lanaudière region of Quebec, Canada. It is over long, and has a drainage basin (watershed) of Its source is the Mont Tremblant massif. Seven significant rivers flow into the Assomption (de la Boule, Versailles, Noire, la Chaloupe, Ouareau, Saint Esprit, and Achigan) before it flows into the Rivière des Prairies at Repentigny, Quebec. About 150,000 people live in the drainage area of this river.

The L'Assomption River watershed overlaps two natural environments, the Laurentian Mountains and the St Lawrence lowlands, which cover about a third of the watershed area. Its relief is a uniform plain with some hills—from —dominated by agricultural lands. The texture of the soil is rather fine and rests on an impermeable argillaceous (clay) base. The Laurentian Mountains form part of the Canadian Shield. They are separated from the lowlands by a well defined escarpment that rises about This escarpment has many waterfalls. The Laurentians Mountains have an average height of in the south and in the north. And there are even mountains of over in the Mont Tremblant massif where the L'Assomption River forms.

From north to south the average slope of the river decreases. The steeper slopes of the highlands create a fast current whereas the lowland flats produces a slower flow. Moreover, the river meanders a lot which is especially evident at the town of L'Assomption, almost completely surrounded by a large loop of the river. The L'Assomption River watershed has 490 lakes of which 24 have a surface area larger than Most of the lakes are in the Laurentian highlands.

The water quality of the L'Assomption River is seriously affected by the area's social economic conditions. Since 1950, the situation has been complicated by the urbanization of the river banks, by diversified agriculture, and by industrialisation along the southern portion of the river. Although the source of pollution has changed since 1950, because of strict environmental laws and the use of water purification equipment, water pollution is still not fully curbed. Over 150,000 people live in the river's watershed in 43 municipalities, of which the most important are Repentigny, Joliette, Le Gardeur, and L'Assomption. In addition, the northern portion of the river's watershed is a popular vacation area, swelling the population by about 45,000 people during the vacation season. The majority of the municipalities take their drinking water from the river and provide it to more than 100,000 people. The drinking water supply to other residences and country cottages, distributed over approximately 90 percent of the watershed area, comes from water wells.

Besides the urban and industrial pollution, agricultural pollution also contributes greatly to the environment's contamination. Agriculture has a dominant position along the river: in 1995 there were 1,305 producers with under cultivation and possessing 73,563 animals. Agricultural pollution takes several forms: direct pollution (discharge of manure directly in the rivers) and diffused pollution (infiltration of fertilizer products in the groundwater). Diffused pollution is difficult to control because it has a multitude of sources throughout the whole region. Yet without a solution to this problem the water quality of the river will never have the desired quality.

OrderLabelMouthCoordinates Length (km)SourceCoordinates Region 1 L'Assomption River Rivière des Prairies 200 L'Assomption Lake Lanaudière 2 Rivière de l'Achigan L'Assomption River 83.8 Lac de l'Achigan Lanaudière 3 Rivière Jourdain Rivière de l'Achigan 19.4 Duquette Lake Laurentides 4 Abercromby Rivière de l'Achigan 10.8 Connely Lake Laurentides 5 Rivière Beauport (rivière de l'Achigan) Rivière de l'Achigan 20 Lac de la Crosse Laurentides 6 La Petite Rivière (rivière de l'Achigan) Rivière de l'Achigan 13 Saint Calixte Laurentides 7 rivière Saint Esprit L'Assomption River 90.4 Huard Lake Lanaudière 8 Ruisseau Saint Georges L'Assomption River 19.2 Saint Alexis Lanaudière 9 Ouareau River L'Assomption River 80 Lac Ouareau Lanaudière 10 Rivière Burton Ouareau River 16.9 Racette Lake LanaudièreLaurentides 11 Rivière Jean Venne Ouareau River 20.9 Lac des Îles Lanaudière 12 Rivière Kenny Rivière Jean Venne 10.4 Heroux Lake Lanaudière 13 Rivière Beaulne Ouareau River 9.2 Beaulne Lake Lanaudière 14 Rivière Dufresne Ouareau River 29.6 Dufresne Lake LanaudièreLaurentides 15 Rivière Rouge (rivière Ouareau) Ouareau River 56.5 Couture Lake Lanaudière 16 Rivière Blanche (rivière Rouge) Rivière Rouge (rivière Ouareau) 17.8 fr Lanaudière 17 Le Grand Ruisseau (rivière Rouge) Rivière Rouge (rivière Ouareau) 15.1 Sainte Mélanie Lanaudière 18 Rivière Trudel Ouareau River 7.6 Chertsey Lake Lanaudière 19 Rivière du Nord (rivière Ouareau) Ouareau River 6.5 Lac du Pin Rouge Lanaudière 20 Rivière Versailles L'Assomption River 12.5 spring Lanaudière 21 fr L'Assomption River 8.7 Lac des Cèdres Lanaudière 22 fr fr 12.6 Vauvert Lake Lanaudière 23 Rivière McGee L'Assomption River 14.4 Marguerite Lake Lanaudière 24 Rivière Lavigne L'Assomption River 16.9 St Amour Lake Lanaudière 25 fr L'Assomption River 14.7 Laré Lake Lanaudière 26 Rivière Noire (Matawinie) L'Assomption River 52.6 Lemieux Lake Lanaudière 27 lt=Blanche River Rivière Noire (Matawinie) 10.8 Lac à Canards Lanaudière 28 Rivière Leprohon Rivière Noire (Matawinie) 16 small lake Lanaudière 29 fr Rivière Noire (Matawinie) 17 Lac à la Pluie Lanaudière 30 fr L'Assomption River 20.6 Lanoraie Lanaudière