Lac St-louis and St. Lawrence beckon, but is it safe to swim?
Chemicals from an industrial past linger in the sediment, and sewage is a worry
As the sun scorched the city and the temperature reached 35 C last month, Montrealers cooled off in the river.
Children played with inflatable toys in Lac St-louis near Pointeclaire village. Along the lakeshore in Dorval, couples dipped their toes in the water and lay on towels near the rocky shore.
Montrealers used to avoid submerging themselves in the waters surrounding the city because of pollution, but the coronavirus pandemic has limited access to pools, pushing greater numbers of people to seek relief from the heat in Lac St-louis and the St. Lawrence River.
The city of Montreal says the water is usually safe for swimming and is tested frequently. But chemicals from an industrial past linger in the sediment, and heavy rains flush raw sewage into the river.
The lake water at one time was clear and popular with swimmers. Crowds of beachgoers in the 1940s and ’50s converged on Pine Beach in Dorval and at other spots along the waterfront. Tourists from Montreal stayed in hotels dotted along Lakeshore Rd. They came to the West Island, which was effectively the countryside, to relax and to swim.
Michel Hébert, the president of the Dorval Historical Society, said the water was clean at the time. “In the ’40s and ’50s, the beach was very popular,” he said. “On Saturday and Sunday, it was full, full of people.”
Then waste made its way downriver from the timber industry, among others, Hébert said. Chemicals, pesticides and metals like mercury contaminated the sediment; sewage dumped directly into the St. Lawrence built up.
The lake began to smell. Testing in the ’60s and ’70s revealed the extent of the pollution and areas that had been popular with weekend bathers were sealed off.
“You couldn’t swim there,” Hébert said. “It was too polluted.”
Industrial contaminants had settled in the silt at the bottom of the lake. Environment Canada found in 2003 that the amount of contaminants in the sediment around the island was beginning to decline. But more recent research has flagged the buildup of new chemicals. Several studies are being conducted into the effects of higher concentrations of these contaminants.
Experts suggested to the Montreal Gazette that swimmers should avoid kicking up sediment lest they ingest potentially harmful contaminants lurking on the lake floor.
The water itself is usually clean, a city of Montreal spokesperson said last month. Samples taken at 25 stations along the shoreline during a June heat wave revealed low concentrations of fecal coliform, a type of bacteria associated with sewage and animal waste. Fecal coliform levels are the standard measurement used to determine whether a body of water is safe for swimming.
The city posts water-testing results online. As citizens took to the water to cool off last month, bright or dark green dots on the interactive map (found at bit. LY/2D8LEL2) marked most testing locations — indicating good or excellent water quality.
But the heat wave broke in spectacular fashion. A storm on June 23 whipped through the Montreal area, dumping rain onto steaming roads and into storm drains and sewers. The water quality in some West Island areas, where swimmers had flocked days earlier, were suddenly considered “polluted,” meaning that fecal coliform levels had climbed as much as tenfold in some cases.
The sudden change in water quality happened because many sections of the Montreal sewage system are old and operate on a “combined” system — rainwater flows into the same pipes that carry raw sanitary waste.
Susan Gaskin, a professor of engineering at Mcgill University who specializes in environmental hydraulics and water resources, said such a system is not designed to handle heavy rainfalls. During storms, she said, excess water overwhelms it, flushing sewage into the St. Lawrence and Lac St-louis.
“As a general rule for a citizen,” Gaskin said, “I would say I wouldn’t swim two or three days after a heavy rainfall, because then the water definitely isn’t going to be as good.”
A key take-away for swimmers wanting to dip into the waters around Montreal is to check the city’s website before you swim. The quality fluctuates drastically at some sites around the island depending on the weather.
“Good” swimming-quality water has fewer than 100 colonies of fecal coliform per 100 ml. At the Pine Beach site in Dorval on Friday, after Thursday’s rain, fecal coliform levels soared to 1,400 colonies per 100 ml, considered well above “polluted” levels.
But generally, Gaskin said, the quality of the water surrounding Montreal has been getting better since the mid-1990s, when the city began treating all its waste water in a plant on the eastern tip of the island, providing favourable conditions for the steady return of wildlife to the shores around the island.
“If you start seeing herons on the edge of the water, then that means you’ve got amphibians,” she said, “and amphibians are the most sensitive to all of these pollutants. So when you see the wildlife start coming back, you know that your water quality, in general, is improving.”
When you see the wildlife start coming back, you know that your water quality, in general, is improving.