After much discussion and disagreement Montreal's big flush is underway.

Four crews went along the southern side of the island overnight to open valves diverting wastewater into the river, while the snowmelt collector near the Bonaventure Expressway began to drain.

Sewage is flowing at two dozen locations, with most of the pipes between 30 and 50 metres offshore.

Workers set up nets or floating booms around those sewer outlets, and crews in boats are using nets to remove particles that float to the surface.

“If there's big residue, big parts, pieces – we pick that up,” said Rochard Kobel of Urgences Marine.

The city of Montreal does not know how much material it will catch in the nets before it floats downstream, but liquids will flow through easily, with CTV reporter Caroline Van Vlaardingen able to see some sort of white film about 100 metres offshore from a sewage pipe in Verdun.

Environmentalist Daniel Green, who was taking his own water samples at the water’s edge Wednesday, said the city got it wrong when it told citizens they wouldn’t see or smell anything.

“It's very visible and you do smell it,” Deputy Leader of the Green Party.

Green maintains the city could have lowered the amount of sewage it discharged into the St. Lawrence.

“They didn't' have to discharge so much,” he said.

Montreal’s opposition party, Projet Montreal, said the mayor didn’t fully consider other possibilities.

“The mayor has decided he would rule this with authority, not with listening,” said Projet Montreal leader Luc Ferrandez.

How to minimize the impact

In order to minimize the impact of the expected 8 billion litres of sewage that will flow into the river, the city is urging citizens not to flush items that shouldn't go into drains and toilets anyway.

That list includes:

  • facial & baby wipes
  • diapers
  • cotton ear swabs
  • hair
  • dental floss
  • tampons
  • condoms
  • medication
  • cooking grease

Avoiding the shoreline

Dozens of signs have been posted near the shoreline in Montreal warning people to avoid the water.

Green warned people that anyone not listening to warnings about the water is taking a huge chance.

“There’s enough coliform bacteria being discharged now along the shoreline that if you touch the water and bring you fingers to your mouth. You will have an effective dose to give you gastroenteritis,” he said.

In Verdun there is a park where many people let their dogs play, and it's common for pets to go into the water.

Julie Chevrier is one owner who will keeping her dog on a leash for at least the next week.

"The water it's just one of her funnest things to do, to go and swim. In the summer she's drinking the water and it's one of her favourite activities," said Chevrier.

"It's not even an option anymore."

Construction work

Construction crews began working in the collector as soon as it was empty, and will be working around the clock until they are done. They expect to finish in seven days at the most.

They are replacing beams that support the roof of the tunnel, because the existing supports are rotting away and have been dropping into the sewage flowing to the city's main treatment plant.

The city of Montreal says if the work is not done one of those rotting beams could badly damage the city's wastewater treatment plant -- leading to a catastrophic failure.

If the treatment plant were damaged, the city estimates it would take weeks to fix, forcing untreated sewage to flow into the river for the entire duration of the repair.

Within two and a half years, Montreal is expected to have a brand new wastewater sewage treatment plant.