A dozen demonstrators were arrested Wednesday as RCMP officers moved in to dismantle a "human drawbridge" that was preventing oil tanker traffic from passing underneath the Ironworkers Memorial Bridge.

The dangling blockade had been in place since before dawn on Tuesday, when the anti-pipeline activists accessed the catwalk below the crossing and seven of them rappelled down in climbing harnesses.

About 36 hours later, a handful of Mounties scaled the catwalk to arrest them in what appeared to be a high-risk and highly technical extraction operation.

North Vancouver RCMP said a dozen people were taken into custody and are facing mischief charges. The activists could also be charged with impeding the safe movement of a vessel under Sec. 121 of the Canada Shipping Act, an offence that carries a maximum penalty of 18 months in prison and a $1 million fine.

One of the demonstrators, who spoke to CTV News from his precarious position under the bridge on Tuesday, said the potential charges have not discourage him from actively opposing Kinder Morgan's proposed Trans Mountain pipeline expansion.

"I will remain the fierce opposition. It is in my blood to protect the water," Will George said in a statement.

Officers from the Vancouver Police Department and the North Vancouver RCMP detachment spent more than a day monitoring the blockade from the sidelines before Mounties took action Wednesday afternoon.

"Public safety is the priority, both for the protesters and for the police," North Vancouver RCMP said of the operation on Twitter.

Later, the detachment described the process of removing the protesters as "tedious and slow" work.

There were still tense moments captured by CTV's Chopper 9 helicopter once the operation was in full-swing. Clad in a harness and helmet, an officer was recorded rappelling down to one of the activists. 

Suspended in air above circling police and Coast Guard boats, the two appeared to exchange words before the Mountie attached something to the demonstrator's harness and returned back up to the catwalk. 

The operation was observed from the south end of the crossing by members of Greenpeace Canada, protest group Protect the Inlet and their supporters.

Hours earlier, the protesters reported being well-fed, warm and comfortable, and said they had "no plans on leaving any time soon." 

Emma Jackson said the dramatic aerial blockade was part of an ongoing response to the federal government's highly controversial $4.5-billion purchase of Kinder Morgan's expansion project.

"It doesn't matter that Justin Trudeau has decided to make taxpayers into the shareholders of this project, it still will not go forward," Jackson said in a Facebook video. "This resistance movement, if anything, is stronger than ever because of this recent decision."

Kinder Morgan did not provide a schedule of tanker arrivals or departures early on in the protest, but has since confirmed that one vessel, the Serene Sea, has been trapped inside Burrard Inlet as a result of the blockade.

Tanker blockade
An RCMP officer hangs below the Ironworkers Memorial Bridge next to an anti-pipeline activist on Wednesday, July 4, 2018.

"A vessel loaded with crude oil departed our Westridge Marine Terminal and is now waiting for suitable conditions at its Port of Vancouver designated mooring location," a spokesperson for Trans Mountain told CTV News in an email.

"We respect the right to peacefully demonstrate and there are many ways to express opinions in a safe and lawful manner. It is unfortunate that the actions of these individuals have caused disruptions to vessels and individuals that transit to and from the waters east of the Ironworkers Memorial Bridge, including customers from our terminal and the other marine cargo terminals."

A spokesperson for Port of Vancouver said deep sea vessels and some other boats, such as sail boats with high masts, were unable to cross underneath the Ironworkers bridge because of the protesters and their banners.

Shorter vessels such as tugboats, barges and small commercial vessels were still able to go back and forth.

With files from CTV Vancouver's Maria Weisgarber