MTL Stats Shores · UTC

Water quality on Montréal's shores

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Can you swim in Montréal?

Every week from May to October, the City of Montréal's aquatic monitoring team (RSMA) takes a water sample at 103 shoreline points around the island: Rivière des Prairies, Lake Saint-Louis, the Laprairie basin, the St. Lawrence River and the Île Bizard marsh. The laboratory counts faecal coliforms, bacteria that reveal contamination by sewage.

The criterion used by Québec's environment ministry and by the QUALO programme is 200 CFU/100 ml for direct-contact activities such as swimming or windsurfing, and 1000 CFU/100 ml for indirect contact such as canoeing or fishing. A point earns its QUALO certification when the geometric mean of its season stays under 200 and at most 10% of the samples exceed that threshold.

How to read this page

The number at the top is the latest value available for the chosen water body or point, with the real sampling date: data stops in October and resumes in May. For a water body, the curve traces the geometric mean of its points at each round; the Share under 200 quantity gives the proportion of points fit for swimming that week. The Specific point menu follows one park or boat ramp in particular.

The coliform axis is logarithmic: the green, amber and red bands are the three quality levels. A spike after heavy rain is normal, as combined sewers overflow into the waterways; the Sewer overflows page shows those episodes. The pesticides of the nearby farm rivers and lead at the tap have their own pages.

Frequently asked questions

Is the data official?: Yes. It is published as is by the City of Montréal on its open-data portal under the CC BY 4.0 licence. MTL Stats aggregates it by round and by water body, without correcting it.
Why is there nothing in winter?: The QUALO programme samples from May to October only. The number shown remains the season's last sample, with its date.
Is a point under 200 an official beach?: No. The criterion describes the bacteriological quality of the water; swimming is only allowed at supervised, equipped beaches.