Montrealers who took part in last week's Grand Splash event at the Old Port unknowingly put their health at risk.

It's an annual event where about 200 people leap into the water to demonstrate for improved access to the waterfront on the island.

According to an independent investigation, fecal coliform levels in the water at the port were 18 times higher than acceptable levels.

Pierre Lussier, a spokesperson for the event, was shocked to learn that water samples showed fecal coliform levels of 3600 parts per 100 ml.

"We had discussions with the city of Montreal and to our knowledge it was safe to swim, so I'm very shocked about the amount of fecal coliform. 3600 has never been seen here," said Lussier.

Fecal coliform levels tend to increase suddenly in several areas around the island following heavy rainfall, and there had been several periods of heavy rain in the week before the Grand Splash. Results from water samples usually come in after 48 hours.

The Lachine Canal had been ordered to close repeatedly throughout July because of heavy rain stirring up sediment, and because of the possibility of overflow from sewers.

Lussier said his organization had reached out to the 200 participants, and two of them reported feeling ill following their swim in the river.

Exposure to certain strains of e. coli bacteria typically produces diarrhea and other gastroenterological distress.

Project Montreal's Alex Norris was among the swimmers at the event.

“I did notice the water was worse than last year when I took part in the event,” he said, adding that the Grand Splash is symbolic, with or without pollution, because it's meant to encourage the city to make its waterfront usable for all Montrealers.

“The city's been dragging its feet in improving the water in the city and also in providing safe swimming spaces in the river for Montrealers,” he said.