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. Geography 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. Hydrography 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. Water quality Urban and industrial pollution 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