Glyphosate and pesticides in the rivers around Montréal

Glyphosate in the rivers around Montréal

Québec's environment ministry samples a dozen farm-country rivers every week from May to September and tests for more than eighty pesticides. The four permanent stations closest to Montréal are on this page: the Saint-Régis River at Saint-Isidore and the Hurons River at Saint-Jean-Baptiste, in corn and soybean country; Rousse Creek at Saint-Joseph-du-Lac, among orchards and market gardens; Point du Jour Creek at L'Assomption, in potato country.

Glyphosate and its breakdown product AMPA have been detected in most samples since the 2010s, as have atrazine and S-metolachlor. The neonicotinoid insecticides (imidacloprid, clothianidin, thiamethoxam) almost always exceed Québec's 0.0083 µg/l criterion, one of the strictest in the world. The number at the top is the latest measured concentration; the badge says where it stands against the limits.

Three limits on every curve

Each chart carries as dashed lines the limit of Québec (blue: the MELCCFP water-quality criterion for the protection of aquatic life, chronic effect, known as CVAC), of Canada (red: the Canadian Council of Ministers of the Environment guideline for aquatic life, long-term exposure) and of the European Union (amber: the 0.1 µg/l per-pesticide parametric value of Directive 2020/2184 on drinking water, as Europe has no common standard for rivers). The first two protect aquatic organisms, the third tap water; their spread, one to eight thousand for glyphosate, shows how different the questions they answer are.

The axis is logarithmic so that both the laboratory's detection limits, around a thousandth of a microgram, and the 800 µg/l glyphosate criterion fit. A sample where the pesticide was not detected sits on the chart floor and is labelled as such.

And at the tap?

Montréal's drinking water is drawn from the St. Lawrence and Lake Saint-Louis, upstream of these farm rivers, and treated at the Atwater and Charles-J.-Des Baillets plants. The City tests fifteen pesticides in its network and publishes the results in an annual PDF report; MTL Stats read them from 2016 to 2025 onto the Tap water page. In ten years, only 2017 shows atrazine and 2,4-D, at 0.3 µg/l; glyphosate has never been detected, but with a detection limit of 10 µg/l, a hundred times the European limit of 0.1 µg/l. Lead at the tap is tracked month by month on the Lead at the tap page.

Frequently asked questions

Do these rivers supply Montréal's drinking water?

No. They flow into the St. Lawrence or the Mille Îles River downstream or away from the intakes. They measure the pressure of farm pesticides around the metropolis, not tap water.

Why does the data stop at last summer?

The ministry publishes a season's results the following year, once the analyses are validated. The page updates as soon as the file is released.

What does "not detected" mean?

That the concentration is below the method's detection limit, often 0.001 to 0.01 µg/l. The point is drawn at the chart floor and counted as zero in the headline number.