Environment Canada says it cannot authorize the sewage dump Montreal is planning to carry out, but won't say whether it has the power to stop the plan from going forward.

The city announced Friday it would go ahead with a plan to dump 8 billion litres of untreated sewage into the St. Lawrence River starting two weeks from now. It had put the plan on hold earlier this week after people complained about the project, but now says it has no choice.

"It's the only possible option," said Pierre Desrochers, president of Montreal's Executive Committee.

In an email to CJAD news, Environment Canada spokesperson Mark Johnson said under the “Wastewater Systems Effluent Regulations,” a set of rules that fall under the Fisheries Act and were enacted earlier this year, the federal environment department “cannot authorize” the type of wastewater deposit Montreal is planning to undertake. The Fisheries Act also prohibits unauthorized deposits of potentially harmful substances that can taint water where fish live.

Johnson stopped short of saying that the federal government has the power to stop the city from proceeding, saying the two levels of government are in communication.

The reason for the raw sewage dump is because a snowmelt collector near the Bonaventure Expressway needs to be moved. The Wellington collector feeds into a major sewer line, and all the pipes leading to that line need to be drained. Once the sewers are clear, construction crews will dismantle the existing snowmelt collector and build a new one.

Quebec's environment ministry approved the plan earlier this year. Environment Minister David Heurtel said this week he was led to believe there was no other way to clear the sewer lines when the plan was approved.

Environmentalist and Green Party candidate Daniel Green says there are agreements in place between Ottawa and Quebec concerning the river and waste water. The question is which level of government takes precedence.

“Ultimately it would be a judge that would have to decide that in a court of law. This is why we are looking at possible legal action to try to have this out before the discharge begins,” he said.

But as far as the opposition at city hall is concerned, the Coderre administration has a big hurdle to jump.

“They need to have both authorization and we know that the federal one, they didn't receive the federal authorization,” said Projet Montreal councillor Sylvain Ouellet.

According to Environment Canada’s website, wastewater is Canada’s biggest source of water pollution. More than 150 billion litres of untreated and undertreated wastewater is dumped into the country’s waterways every year. City officials have said the amount of untreated waste flowing into the river is negligible compared to the amount of water that flows through the St. Lawrence.

People are being asked to avoid the water on the southeast shores of the island from Oct. 18, when the operation was slated to start, to the 28. In the Old Port that restriction will last until Nov. 15.