Canada's government has downgraded the protection of North Pacific humpback whales in order to allow the $7.9 billion Northern Gateway pipeline project to go ahead.

The decision has changed humpback whales status as "threatened" to a "species of special concern" under the Species At Risk Act (SARA).

The legislation for endangered species that prevented the pipeline project from progressing stated that "no person shall destroy any part of the critical habitat of any ... listed threatened species".

Now that the humpback's status has been reclassified, the whales will no longer be "subject to the general prohibitions set out in SARA, nor would their critical habitat be required to be legally protected under SARA," according to the Vancouver Sun.

The pipeline is planned to transport 550,000 barrels of crude oil from Alberta to Kitimat in British Columbia, with approximately 250 huge tankers entering and leaving Kitimat every year.

Environmentalists have said that the pipeline could put the mammals in greater danger because of the increased amount of large vessels that could collide with the whales, potential oil spills and excessive noise.

Environmental group Ecojustice said in December that a panel's conditional approval of the pipeline project ignored the legal protection of humpback whales, whose population on the west coast of Canada falls in the "low hundreds", according to the Canadian government.

The humpback is among the largest mammals in the world, growing up to 14 metres in length and weighing up to 40 tonnes.

Following the report and the reclassification of the whales' status, a decision on the pipeline is set to be made in June.