An environmental group fearing harm to marine mammals like this blue whale has lost its court bid to prevent seismic testing off Vancouver Island. (Gretchen Steiger/Cascadia Research)

An environmental group has lost its legal fight to stop a U.S. government research ship from entering Canadian waters off the west coast of Vancouver Island.

Ecojustice wanted to stop the ship from performing seismic testing in the ocean, but in a decision issued Thursday, the Federal Court rejected the group's bid for an emergency injunction.

The court instead accepted the opinion of an expert at the Department of Fisheries and Oceans who said the seismic blasts would not harm marine mammals such as whales and dolphins.

Columbia University researchers planned to spend a month aboard the ship Marcus Langseth, mapping the sub-surface of the sea floor where earthquake-causing tectonic plates diverge.

The ship's 36-gun towed seismic array would send blasts into the water every couple of minutes, which would create a noise as loud as an army artillery piece going off, according to Ecojustice.

The group said the proposed seismic tests would threaten endangered whales in the Endeavour Hydrothermal Vents — a protected Canadian marine area about 250 kilometres off the coast of British Columbia.

But in court on Aug. 25, lawyers for Foreign Affairs Minister Lawrence Cannon said Ottawa had asked for and received various "mitigation measures" from the university.

Researchers have agreed to reduce the maximum sound level of seismic charges from 180 to 160 decibels.

Also, a number of federally approved observers will be aboard the vessel to ensure no marine mammals such as whales are within 7.7 kilometres of the ship during the blasts.