The St. Lawrence River contains several unique ecosystems, all interconnected. From Lake Saint-Louis near Montreal to the Magdalen Islands, a vast network of habitats forms a delicate balance that allows thousands of plant and animal species to thrive. Here are a few of the ecosystems that make the St. Lawrence River such a special place.
Aquatic Plant Beds
Aquatic plant beds are areas dominated by floating or submerged plant species. These ecosystems serve as habitats for many species of fish and invertebrates. They are also essential feeding grounds for migratory birds during their biannual journeys. Along with swamps, bogs, and marshes, aquatic plant beds are part of St. Lawrence’s wetlands and act as natural filters that improve water quality. These habitats are home to the beautiful Iris versicolour, the official flower of Quebec.
Salt Marshes
The St. Lawrence features a unique ecosystem known as salt marshes—wetlands that are influenced by tides. Due to extreme variations in salinity, temperature, and oxygen levels, these complex environments have forced many plant and animal species to adapt. Salt marshes play a vital role by protecting against floods, filtering and improving water quality, and capturing carbon. They are also stunning natural sites that attract nature lovers and outdoor enthusiasts.
An Estuary, a Gulf, and a Fjord
Near Île d’Orléans, where freshwater from the Great Lakes and rivers meets the salty waters of the Atlantic Ocean, the river becomes a vast estuary. Further downstream, near Tadoussac, the salinity and depth of the river give it marine characteristics. This is one reason why whales and belugas are found here, drawing many tourists each year. It is also where the majestic Saguenay Fjord flows into the river. Surrounded by cliffs, the fjord is so deep that it too attracts large marine mammals. About 250 km further downstream, this vast estuary—one of the largest in the world—becomes the Gulf of St. Lawrence. This inland sea, bordered by the four Maritime provinces, eventually flows into the Atlantic Ocean. At the heart of this sea lay the Magdalen Islands and their sandy shoals, teeming with fish and shellfish.
