Want to go for a dip? Montreal’s swimming water quality varies from east to west

Those wanting to beat the heat by jumping into the water on the shores of the Island of Montreal may want to think before making a splash, as water quality varies dramatically based on where you are.

Water quality on around 40 per cent of Montreal’s shorelines contains troubling levels of pollutants, with most of those in the east.

The Aquatic Environment Monitoring Network (RSMA) uses the QUALO program to measure the bacteriological quality of the 103 measuring stations on the Island of Montreal.

In 2024, 62 of these (60 per cent) were approved for swimming, two per cent less than the 10-year average.

One station at Pierrefonds-Roxboro was deemed “unsanitary,” three in Riviere-des-Prairies--Pointe-aux-Trembles were listed as “polluted”, 19 were rated “bad,” and 18 stations “sometimes bad.”

A year prior, one station was unsanitary, two were polluted, 15 bad and 17 sometimes bad.

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To be approved, the station must not exceed 200 coli per 100 millilitres, and no more than 10 per cent of samples can exceed 400 coli per 100 millilitres during a sampling season.

“Coli” means fecal coliforms (E.coli: bacteria found on plants, in soils, water and the intestines of humans and warm-blooded animals) that are found in the water.

Those that received poor designations were predominantly on the island’s north shore (22 stations), while just one was in the southwest and six in the southeast.

None of the stations between Sainte-Anne-de-Bellevue and Montreal East along the south shore received negative ratings.

Along the Saint-Lawrence River, there are 16 measuring stations.

Last year, 75 per cent of them were approved for swimming and recreational activities. This year, the number was 69 per cent, which is still above the five-year average of 53 per cent.

Ile Bizard-Sainte Genevieve (88 per cent), the La Prairie Basin (88 per cent), and Lac Saint-Louis (60 per cent) were all over 50 per cent safe, while just 41 per cent of Riviere des Prairies’ 37 stations obtained a safe QUALO rating.

Fondation Rivieres produces a map showing 57 places that could be accessible for swimming.

Again, the majority of those places are on the west of the island, with just five spots east of the Ville-Marie borough suitable for swimming.

Inland water

When it comes to streams and inland bodies of water, 60 per cent were rated as either polluted (45 per cent) or bad (15 per cent), according to the RSMA.

The monitoring stations at the Lachine Canal and the pond at Docteur-Bernard-Paquet Park were the only of 53 inland stations where the water quality was excellent. Nine others were listed as good.