Celebrity environmental activist Erin Brockovich has chimed in on Montreal's pending sewage dump, calling the plan to dump eight billion litres of raw sewage into the St. Lawrence River "ridiculous and shameful."

Brockovich is part of the growing public outcry over the controversial plan that has been described as "the lesser of two evils" by Montreal officials.

In a Facebook post, Brockovich encouraged others to contact Montreal Mayor Denis Coderre directly, to voice their concerns.

An online petition opposing the dump has collected more than 80,000 signatures as of Wednesday afternoon.

The plan has been raising a lot of concerns for many Montrealers – but even more for those living downstream.

Scientists say the untreated sewage will flow all the way to Quebec City, but most of it will settle near Sorel, Que., in the Lake Saint-Pierre basin of the St. Lawrence.

Boaters like David Lavallee say the water there is far from clear blue but he's concerned it could get worse after the proposed sewage dump.

So far, Coderre has tried to downplay the consequences of the dump, pointing to similar plans in 2003 and 2005.

But according to researchers at Quebec's National Institute of Scientific Research, there is reason to be concerned.

"We know there are effects on fish and we know that there are effects on the reproductive functions and some of these are quite dramatic," Daniel Cyr told CTV Montreal on Wednesday.

Ten years ago, Cyr was at a basin of the St. Lawrence where sewage was ending up. He found the fish in the area were losing their ability to reproduce.

"One third of these spottail shiners have ovaries growing in the testes," he explained.

And with the pending sewage dump, Cyr believes the problem could get worse.

"We're going to increase the bacteria load," he said. "We're going to increase the viral load – everything goes into the water."

He adds the plan will not only affect many generations of fish, but potentially humans as well.

"Many years ago, we were fishing at a site where we were seeing effects on fish and if we fed the fish to rats, we were seeing effects the reproductive system of rats," he said. "So is this happening to humans? I don't see why there isn’t a good chance that it would be happening."

No one knows for certain what the long-term impact of the plan will be. Scientists say part of the reason is because over the last 10 years, the budgets to study lakes and rivers have been severely cut.

"(There have been) a few little studies here and there, but nothing really major to follow-up and really judge the health of the St. Lawrence," Cyr said.

Meanwhile, Quebec Premier Philippe Couillard says the city can't afford to hold off on the sewage dump any longer.

"If someone has an idea of genius that has not been mentioned until now, fine," Couillard told reporters on Wednesday. "But until now each time we've looked at this and Mayor Coderre and his team have looked at this, we always come to the same topic."

On Tuesday, federal Environment Minister Leona Aglukkaq issued a statement asking Coderre to put the plan on hold until Ottawa assess the environmental impact of the proposal.

Coderre said he would give Environment Canada officials three days to come to Montreal to discuss the plan.

"If they want to be serious about it, they don't want to play politics … they want to be responsible and accountable, sit with us and we'll find a solution," he said during a news conference Tuesday.

Beginning Oct. 18, a major sewer line will be cleared into the St. Lawrence River over a period of seven to 10 days.

Officials have said the sewage dump is necessary in order to continue construction work on the Bonaventure Expressway.

With files from CTV Montreal

Correction: A previous version of this story incorrectly reported Montreal had conducted a sewage dump in 2007.