Montreal, Canada - Thousands are expected to march through a city in western Canada in what organisers say may be the largest showing of "clear opposition" to a contentious oil pipeline project in recent memory.

Indigenous activists will be marching on Saturday alongside environmental groups, local residents and other supporters in Burnaby, a town in the province of British Columbia (BC), against plans to expand the Trans Mountain pipeline.

Approved by Canadian Prime Minister Justin Trudeau in 2016, the expansion would twin the existing Trans Mountain pipeline, operated by Texas-based oil giant Kinder Morgan, which stretches 1,150km from the Alberta tar sands to the coast of BC.

The expansion - which would increase the pipeline's capacity from 300,000 to 890,000 barrels of oil a day - has faced staunch opposition, especially from indigenous communities.

"There comes a time in your life when you have to stand for something," said Ta'ah Amy George, a Tsleil Waututh elder and one of the organisers of Saturday's march, which she said is expected to draw as many as 10,000 people.

The Tseil Wauhtuth (meaning "People of the Inlet") have lived on lands near the Burrard Inlet in southern BC for tens of thousands of years, George told Al Jazeera.

She said the community fears an oil spill will harm everyone living in the area and the large oil tankers that are expected to come into the inlet to transport oil would destroy local marine life.

"It's not if there's a [spill], but when there's a [spill]," George said.

"Our ancestors protected this inlet and this little piece of land that we got left with. They protected it for us … We're thinking of our [next] generations: my children and grandchildren and I have great-grandchildren."

890,000 barrels a day

The $5bn Trans Mountain expansion project aims to get Canadian tar sands oil to new markets in Asia.

Kinder Morgan, the company behind the project, says the pipeline expansion will create short and long-term jobs and increase tax revenues at the provincial, federal and municipal levels.

"We support the right to peacefully and lawfully express opinions and views about our project and we understand that not everyone supports the expansion," a Trans Mountain spokesperson told Al Jazeera in an email.

"We're confident we can build and operate this project in a way that respects the values and priorities of Canadians and in respect of the environment."

Our ancestors protected this inlet and this little piece of land that we got left with. We're thinking of our [next] generations. Ta'ah Amy George, a Tsleil Waututh elder and one of the organisers of Saturday's march

Construction at the Westridge Marine Terminal in Burnaby began last September, while additional "preparatory work" on the same terminal and the Burnaby Marine terminal - the end point of the pipeline - began earlier this month, the spokesperson said.

"The project will provide the needed transportation capacity for Canada's resources to access global markets and maximise benefits to all Canadians including local, regional and Aboriginal communities," the spokesperson added.

But a widespread, indigenous-led movement has mobilised against the project for several years, while environmental groups have also spoken out against the potential ramifications of an oil spill.

"Kinder Morgan wants to bring more than 400 supertankers into the BC harbour every single year," said Mike Hudema, a climate campaigner with Greenpeace Canada. "If one of those is to have an incident … you're talking about widespread damage throughout the marine ecosystem," he told Al Jazeera.

Most of the oil being produced and transported in Canada is called diluted bitumen, which is particularly difficult to clean up because it tends to sink in water, Hudema explained.

He said a spill could "exterminate" the already endangered killer whale population living in the coastal waters and "the damage could be catastrophic and could last for decades, if not longer."

Hudema said that over a dozen lawsuits have been filed against the project by First Nations and environmental groups.

"The science is very clear," he said, "We can't be building new fossil fuel infrastructure and maintain a climate-safe planet at the same time."

Provinces divided

While the Trans Mountain pipeline has received the green light from the federal government, it has divided some Canadian provinces.

In late January, the BC government passed new regulations that would make it more difficult to transport oil through the province in an effort "to improve preparedness, response and recovery from potential spills".

The restrictions would be in place "until the behaviour of spilled bitumen can be better understood and there is certainty regarding the ability to adequately mitigate spills", the provincial government said in a statement.

The measure was seen as a blow to Trans Mountain and highlighted increasing tensions between BC and Alberta, the province that is home to Canada's tar sands and supports the project.

The science is very clear. We can't be building new fossil fuel infrastructure and maintain a climate-safe planet at the same time. Mike Hudema, a climate campaigner with Greenpeace Canada

Representing the third-largest crude oil reserves in the world, after Saudi Arabia and Venezuela, the Canadian tar sands cover over 142,000sq km in northern Alberta.

In 2016, about 2.5 million barrels of crude bitumen were produced daily after an energy-intensive and expensive extraction process, the Alberta Energy Regulator estimated.

While proponents of the Trans Mountain project in Alberta tout its economic impact, the BC government, a coalition between the left-leaning New Democrats and the Green Party, had previously vowed to block its expansion.

Several cities in BC, including Vancouver and Burnaby, have also voiced their opposition to the project.

'Clear opposition'

Despite the opposition, the federal government has remained steadfast in its support for Trans Mountain.

"Approval of the Trans Mountain Expansion was based on facts, evidence and what was in the national interest," a spokesperson for Natural Resources Canada, a government ministry, told Al Jazeera.

Ottawa approved the project "subject to 157 legally binding conditions" that "will address potential Indigenous, socio-economic and environmental impacts", spokesperson Jerri Southcott said in an email.

"Throughout the construction and operation of this project, Indigenous voices will be heard. Their counsel will be sought and their knowledge valued," Southcott added.

In early February, Prime Minister Trudeau said his government would not be able to meet its commitment to fight climate change or implement a plan to protect oceans from oil spills, without first getting the Trans Mountain project built.

If people think this is something [that] people are going to easily give up on … that's sadly mistaken. People have drawn a line in the sand and this really is only going to build. Andrea Harden, energy and climate justice campaigner at The Council of Canadians

"The only way we can get any of those things is if we do all three of those things together," Trudeau told CBC Radio.

"As I've said for a long time, we need to make sure we're both protecting the environment and growing the economy at the same time."

Andrea Harden, energy and climate justice campaigner at The Council of Canadians, a progressive non-profit group, accused the Trudeau government of "speaking out of both sides of its mouth".

On one hand, the prime minister has signed on to the Paris Climate Agreement to combat greenhouse gas emissions, while on the other backing intensive oil and gas projects like the Trans Mountain pipeline, Harden told Al Jazeera.

Science and facts have been ignored "in terms of both this pipeline being out of tune and inconsistent with our [climate] commitments … as well as the very legitimate questions around the safety of shipping diluted bitumen through pipelines", she said.

She said Saturday's march is "another manifestation of the clear opposition" to the Trans Mountain pipeline.

"If people think this is something [that] people are going to easily give up on … that's sadly mistaken," Harden said. "People have drawn a line in the sand and this really is only going to build."