MONTREAL -- Work continues on the REM light rail line to the Trudeau Airport is continuing and while those behind the project believe they've found a way to protect wetlands the line will pass through, environmentalists are not pleased.

The St. Laurent Wetlands is a delicate ecosystem that is home to many species of birds. Environmentalist Lisa Mintz said initial plans would have seen a track go right over the wetlands but a compromise was reached: drilling under the wetlands with a massive tunnel boring machine.

Work to build the tunnel will go 40 meters down and three kilometres across. Work on the tunnel began last week and is scheduled to last until 2021.

“Each time the machine is advancing, it's also putting in the frame of the rings that will compose the future tunnel for the REM,” said Jean-Vincent Lacroix, spokesperson for the project.

Lacroix said this is the first time the boring machine has been used in Quebec and the intention is to preserve wildlife in the area.

“We want to make sure we don't have any impact on the wetlands,” he said. “That's why the boring machine will do all the work underground without having any impact on the surface.”

But Mintz and a group of fellow environmentalists have been pushing the government to re-route the REM line away from the wetlands completely.

“They swear this drill is not going to cause any vibrations but the noise they're already making has driven off a lot of birds that use the area for their migration,” she said.