Montreal Mayor Denis Coderre is firing back at the federal government for 'playing cheap politics,' after it asked Montreal not to dump untreated wastewater into the St. Lawrence River for a week.

Intergovernmental Affairs Minister Denis Lebel made the request Tuesday afternoon, less than two weeks before the sewer work will begin.

His request comes several days after Environment Canada said it was not authorizing the city to dump sewage, but did not say if it could stop Montreal.

"It's unusual to stop an election campaign and come out and make this type of ministerial appearance, but many people are very passionate about this," said Lebel.

The city of Montreal says it doesn't want to dump sewage, but has no choice but to allow unfiltered wastewater to flow into the river for a week while it works on a snowmelt collector near the Bonaventure Expressway.

Montreal Mayor Denis Coderre sounded incensed responding to the issue Monday afternoon, saying officials have been providing all the information on the issue for the past 18 months, and this was nothing more than “playing politics” for the Conservative government, something he knows plenty of in his career as a federal Liberal politician.

Nevertheless, the said federal ministers were welcome to come within the next three days to go over the paperwork again.

“Okay they decide to play politics? They want to sit with us? No problem. I know one thing, David Heurtel did his homework, the ministry of the environment of Quebec did their homework, because we’re all working with the experts and we’re providing all the tools and all the answers that they need, all the paperwork that they need.

He took a swipe at the environment minister and the Conservatives, whom he insulted with a colourful reference to a children's show.

"If the government of Canada -- who is really credible in matters of science and who think 'The Flintstones' are a documentary -- are trying give us lessons to win political points," he mused, "I am not getting into it."

Coderre acknowledged the federal government had the power to block the city's plans.

Coderre also dismissed criticism from the NDP, who's leader Tom Mulcair said Tuesday on the federal election campaign trail that if elected prime minister he wouldn't allow the city to dump the wastewater.

"My dear Tom," he said, "we did all our homework. And the only possible option is this."

Coderre wasn't able to fully explain why he said there would be "no impact" on the St. Lawrence River after the dumping.

He answered: "Because the experts said so."

"Because of the oxygen that goes through the (water) flow," he said. "The waste can eventually be collected. There is dilution, there are some ways that nature is working. We eventually collect all our waste."

The plan to lower the elevated highway to ground level means a snowmelt collector has to be moved. In order to do that, the sewage lines need to be cleared for a week.

Environment Quebec approved the plan, reluctantly, after determining that the city of Montreal had no other option but to allow the short term dumping.

This week provincial environment minister David Heurtel said if the snowmelt collector was not moved the events could be catastrophic, and could include causing long-term damage to Montreal's sewage treatment facilities.

The amount of untreated sewage projected to flow into the St. Lawrence River is 8 billion litres over the course of seven to ten days -- or about the same amount as flows past any given point in the river in about half an hour. 

Federal Green party candidates in Quebec have called the city's decision "ill-advised," suggesting it could have done better.

Daniel Green, a Green candidate, said parsing the work over a longer period instead of proceeding with a one-shot deal in October could have lessened the impact, as would having the work done in February, when, he claimed, frigid temperatures would kill off bacteria.

Coderre has also dismissed concerns raised by a U.S. state senator from New York, Patty Ritchie, who wrote a letter to the International Joint Commission -- whose mandate it is to protect the St. Lawrence and Great Lakes -- to probe Montreal's decision.

Ritchie said the notion of dumping "the equivalent of 2,600 Olympic-sized swimming pools filled with wastewater" from homes and businesses needs further study.

Coderre insists the plan is the right one.

"When you're factual, when you look at the experts, at the end of the day that was the decision to be taken because it was the only one," he said.

With files from The Canadian Press