Apprendre le Québec

The St. Lawrence River

The St. Lawrence River is one of the largest waterways on our planet. At 1,197 km long, its estuary is the largest on earth with a width of 48 km and a length of 370 km. Its watershed covers 1.6 million km 2 and its entire watershed alone represents more than 25% of the fresh water reserves of the entire earth.

Rising from Lake Ontario in Kingston, its flow increases more and more as it advances towards the Gulf, fed throughout its course by its 244 tributaries in Quebec territory. Its main tributary, the Ottawa River, is located at the height of Montreal and increases its flow by more than 2,000 cubic metres per second. At the height of Trois-Rivières, the St. Maurice River contributes an average increase in its flow of 660 cubic metres per second. Then, at the height of Quebec City, are added the Chaudière River and the Montmorency River: at this height, the St. Lawrence River has an average flow of more than 12,000 cubic metres per second.

The St. Lawrence River Valley is home to more than 70% of Quebec’s population and has several hundred municipalities. At least forty of them get their drinking water directly from the river, including Quebec City and Montreal. The latter invest a lot of effort and money to improve the quality of the river’s water: recently, these efforts were rewarded and allowed the reopening of swimming in the river at the height of Parc de la plage Jacques-Cartier, in Quebec City.

Not far from there, upon reaching Quebec City, the river divides in two at Île d’Orléans and gradually widens to reach 15 km at Cap Tourmente and 25 km at Île aux coudres. The eastern tip of Île d’Orléans marks the very beginning of salinity in the water of the St. Lawrence River. At this point, the water is called brackish because it contains very little salt, and becomes truly salty a little after Baie St-Paul.

From Montreal to Trois-Rivières, the St. Lawrence is rather calm and is not affected by the tides. However, past the mouth of the St. Maurice River, the flow of fresh water and salt water reverses with the tides. In winter, we therefore observe a most interesting natural phenomenon between Trois-Rivières and Quebec: although the water is fresh and can therefore turn into ice, the action of the tides perpetually hinders the establishment of a solid and stable ice floe. Since the tides influence the water level on a daily basis, the landscapes of the river around Quebec City are constantly changing, with the snow and ice cover along the river constantly shifting and changing. The dynamics of the tides combined with the impressive flow of the river tear apart the fragile ice cover and deposit new icebergs on the banks every day, like a glacier leaving behind erratic blocks after its passage. Certainly, contemplating such a spectacle under a sunset is an experience that will leave no one… cold.