A container ship is being detained at the Port of Montreal and an investigation is underway after the ship allegedly dumped tonnes of oily bilge waste in Canadian waters.

Third engineer Domingo Silva took a video of the bilge tank bypass. (CBC)

The allegations came to light after a crew member of the MSC Trinidad handed over video evidence to authorities on shore.

The ship is believed to have intentionally dumped its bilge off the coast of Newfoundland. The bilge is a mix of ballast water and oil from ship engines.

Crew members told CBC News that a pipe had been installed on the ship to bypass the bilge tank in order to dump directly into the ocean.

Third engineer Domingo Silva took a video of the bilge tank bypass as evidence.

"I know it's against the law. It's better to complain now than be arrested and have bad reports made against us," Silva told CBC News.

"It may be the destruction of my career," Silva said.

'It is fantastic that anybody would do this'

Bill Montevecchi, a St. John's scientist and a world-recognized authority on seabirds, said Canadians should applaud Silva and his crewmates.

Bill Montevecchi: 'We just need people to rise to the occasion and report it, and here's a gentleman that's risked his career to do that.' (CBC)

"He's a national hero. I think it is fantastic that anybody would do this," said Montevecchi, who has been studying the consequences of bilge-dumping for three decades.

"It's an illegal activity and we just need people to rise to the occasion and report it, and here's a gentleman that's risked his career to do that."

Bilge dumping often results in oily seabirds washing ashore in places like southern Newfoundland, where beaches have often been strewn with birds cloaked in dark, thick muck.

Montevecchi said this is a particularly bad time of year for ocean dumping, as many seabirds that breed in Eastern Canada are now just returning to their colonies.

Convictions against ships that dump bilges, though, are rare. While penalties can theoretically reach more than $1 million, as well as three years in prison, enforcement is difficult, in large part because the evidence of dumping often does not materialize for several days.

The highest fines levied in Canada in a single case involved a 2004 conviction. The fines totalled $170,000.

"It's an ongoing problem. It's been on the go for years and years," said Bernard Martin, a small-boat fisherman working in Petty Harbour, just south of St. John's.

"I think the guy should get a big reward for his courage. I mean, it took a lot of courage to step forward and say what happened, to tell what happened," said Martin. "Maybe that's what we need, too, some kind of financial incentive for whistleblowers."

Sailors approached advocacy group

The MSC Trinidad arrived at the Port of Montreal on Monday.

That day, five sailors contacted the International Transportation Federation, the group that represents sailors, with allegations of illegal dumping.

The ship is operated by the Mediterranean Shipping Company, which has its headquarters in Port-of-Spain, Trinidad.

The company's website says the privately-owned operation was founded in 1970 and is "one of the leading global shipping lines in the world."

Transport Canada investigators are inspecting the vessel, looking for evidence.

In developing countries, bilge is bought and used as fuel, but not in Canada, Patrice Caron from the International Transportation Federation told CBC News. "In Canada, it's considered more like waste and pollution, so we charge the ship owners to take their sludge."

Caron said there is tension on the ship after some crew members blew the whistle on the dumping.

He told CBC that the ship's captain has reportedly urged the sailors to change their story many times.