The St. Lawrence River, the lifeblood of Quebec and Canada, is at a crossroads. At a time when the effects of climate change are becoming increasingly tangible, this rich and fragile ecosystem is showing alarming signs of deterioration. A brief recently published by the Réseau national des conseils régionaux de l’environnement du Québec (RNCREQ) sounds the alarm: without rapid intervention, the ecological, economic and social impacts could be considerable.
Warmer and warmer waters
In recent years, scientists have observed record-breaking warming in the deep waters of the St. Lawrence. In 2022, the temperature at a depth of 300 meters in the estuary exceeded 7°C, a first. This warming is not insignificant: it modifies local ocean circulation by increasing the inflow of warmer, less oxygenated waters from the Gulf Stream, to the detriment of the cold, oxygen-rich waters of the Labrador Current.
These changes influence the entire marine food chain. Some species see their habitat restricted or become more vulnerable to disease. In other words, the rising temperature of the St. Lawrence River is weakening its entire ecosystem.
Hypoxia: a river on its last legs
The lack of dissolved oxygen in the deep waters of the river, known as hypoxia, is another indicator of environmental deterioration. According to the data compiled in RNCREQ’s brief, oxygen saturation in the deep waters has fallen below 15% since 2020, compared with around 40% in the 1930s.
This oxygen deficit is exacerbated by eutrophication: excess nutrients, mainly from agriculture and wastewater, promote the proliferation of algae. When these algae die, their decomposition consumes large quantities of oxygen, exacerbating the hypoxia. The result: aquatic fauna struggles to survive, threatening the river’s biodiversity.
Biodiversity under pressure
The St. Lawrence is home to many emblematic species, including the endangered St. Lawrence beluga. Warming water temperatures, combined with noise and chemical pollution, are making their survival even more precarious. Other species of fish and invertebrates are migrating to colder waters or seeing their reproductive cycles disrupted.
The gradual disappearance of certain species could unbalance the entire marine ecosystem and have major economic repercussions for local fisheries.
Wetlands in retreat
RNCREQ’s brief also highlights the rapid degradation of wetlands along the river, particularly in Lake Saint-Pierre. These areas are essential: they filter pollutants, protect against flooding, host abundant wildlife and act as carbon sinks.
Yet these environments are increasingly being eroded by intensive agriculture, urban development and the absence of vegetated riparian buffer strips. The lack of effective legislative protection leaves these habitats vulnerable to a silent demise.
Saline intrusion: a threat to drinking water
Global warming is altering not only temperatures, but also river flows. A decrease in flow combined with a rise in sea level could cause the saltwater front to move towards cities such as Quebec City and Lévis. This intrusion of salt water into freshwater zones could compromise the drinking water supply of hundreds of thousands of people.
RNCREQ’s brief calls for rigorous studies and investment in infrastructure to guard against this threat.
Act now: RNCREQ recommendations
In light of these worrying findings, RNCREQ proposes several courses of action:
– Strengthen independent scientific research on the state of the river.
– Better align public policies on the environment, urban planning and marine transportation.
– Actively involve First Nations in decision-making processes.
– Protect and restore wetlands, by creating effective buffer zones and promoting sustainable agricultural practices.
– Reduce greenhouse gas emissions at source to slow global warming.
A river to preserve for future generations
The St. Lawrence River is not just a waterway or a source of water: it is a symbol of identity, a pillar of biodiversity and a key element in Quebec’s climate resilience. Its degradation, accelerated by climate change, is a collective challenge.
For those of us who advocate an ecological transition based on scientific rigor, this challenge must be translated into concrete actions to raise awareness, adapt and reduce emissions. The St. Lawrence deserves more than a concerned look: it deserves a sincere commitment.
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Sources:
RNCREQ comments on the provisional terms of reference for the regional environmental and social assessment of the St. Lawrence, March 2025. This brief was produced by the Réseau national des conseils régionaux de l’environnement du Québec (RNCREQ) as part of the consultations surrounding the strategic environmental assessment of the St. Lawrence River.
