Water quality influences the health of ecosystems, recreational uses, and drinking water supply. Several watercourses and lakes show signs of degradation: presence of contaminants, algal blooms, and declining biodiversity.

For over 15 years, the OBV Rivière du Nord has been monitoring the watershed through its water quality monitoring program to assess the condition of surface waters.

Poor water quality

Data from the iEAU platform reveals a gradual deterioration of water quality from north to south in the Rivière du Nord watershed. Since 2016, monitoring stations have shown a decrease in the bacteriological and physico-chemical quality index (BPQI), reflecting an increase in concentrations of fecal coliforms, phosphorus, and nitrogen.

The territory’s lakes are also affected: increased turbidity, the presence of cyanobacteria, and nutrient enrichment demonstrate the accelerated aging of the aquatic ecosystems (eutrophication).

Did you know?

Since 2010, more than 50 stations in the Rivière du Nord watershed are sampled annually to monitor water quality. The results are accessible on the iEAU interactive platform, allowing the identification of the most sensitive areas and guiding protection actions.

Location within the territory

In the Rivière du Nord watershed, water quality is generally better at the headwaters of waterways than at their outlets. This gradual degradation can be explained partly by the use of the territory and the nature of the soils in the St. Lawrence Lowlands, which are more vulnerable to erosion and sediment transport. Since 2010, the OBV Rivière du Nord’s Water Quality Monitoring Program has allowed tracking of this evolution and identifying the most sensitive zones.

The watershed covers nearly 2 223 km² and features high urban density in the south, approximately 180 km² of agricultural land, and a soil sealing rate ranging from 7.6% to 8.6%. There are 21 wastewater treatment plants, 129 overflow structures, numerous septic systems, and more than 450 dams, mainly used for recreational purposes. The most affected regions are located in downstream areas, particularly the Rivière du Nord between Saint-Jérôme and Lachute, the Rivière Rouge (Saint-André region), and several lakes in densely populated residential areas , including Lacs Masson, Raymond, and Saint-Joseph.

Consult the interactive portrait and browse through the different layers to discover the quantity and location of the causes of poor water quality.

Main causes

The causes of water quality degradation are multiple and interconnected, arising from both natural processes and human activities in the territory.

Natural and physical phenomena such as erosion, runoff, flooding, the geological and geochemical composition of the territory, as well as forest fires contribute to the transport or presence of natural and anthropogenic contaminants in surface water and groundwater.

The presence and concentration of wildlife, particularly during migration periods, may increase the microbiological contamination of watercourses through their excrement.

Agricultural activities, particularly the tilling of clayey soils, the use and storage of fertilizers and pesticides, and the management of residual matter, contribute to pollutant runoff and erosion, directly affecting water quality in the watershed.

Urbanization, road networks, faulty septic systems, and municipal wastewater discharge collectively contribute to the influx of chemical and bacteriological contaminants into watercourses and groundwater in the watershed.

Industrial activities in the territory, including landfills, pulp and paper mills, forestry and mining, and contaminated sites, generate various discharges and sediment which may contain metals, nutrients, and organic compounds that degrade surface water and groundwater quality.

Recreational tourism activities, including vacation homes, all-terrain vehicles, ski areas, and golf courses, contribute to soil impermeabilization, runoff, erosion, and the influx of contaminants (sediment, nutrients, chemicals) into water bodies in the watershed.

Artificial water reservoirs, inadequate shoreline development, and the various land uses contribute to altering water regimes and increasing the vulnerability of water of bodies to nutrient enrichment and diffuse contamination.

Climate change

Anticipated climate changes in the Laurentian region are likely to increase the frequency and intensity of extreme weather phenomena, such as heavy precipitation, drought periods, and winter thaws. These variations could accentuate runoff, bank erosion, wastewater overflows, increased use of de-icing salts, and the transport of contaminants into watercourses.

Consequences 

Environmental

  • Decline in aquatic biodiversity (fish, invertebrates, plants)
  • Disruption of food chains
  • Degradation of habitat quality

Social

  • Risks to human and animal health
  • Risks to drinking water supply
  • Restrictions on water-related activities and recreational uses

Economic

  • Revenue loss linked to restrictions on recreational tourism
  • Reduced waterfront property values
  • Increased drinking water treatment costs

Prioritized issues

Water quality is among the six priority issues identified in the 2024-2034 Water Master Plan. For more information, consult the diagnostic sheets. These present the portrait and diagnosis of the issues related to water resources in our territory.

Overconsumption of water resources

Poor water quality

Competing water uses

Degradation and/or destruction of wetlands and aquatic environments

Shoreline erosion

Flooding in at-risk areas

Learn more about the ZGIE du Nord, its strategic planning, and the actions planned to ensure sustainable water management.

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An innovative solution

To meet the needs of water stakeholders, the OBV de la rivière du Nord has developed VigieNord, a citizen science platform that makes it easy to report and geolocate water-related issues. The tool makes a tangible contribution to:

Promote better sharing of field observations among water stakeholders

Identify opportunities for action in the region