Indigenous groups on both sides of the Canada-U.S. border are speaking up about the Keystone XL pipeline, which has recently been given a green light by the Trump administration.

The 2,735-kilometre pipeline project by Calgary-based TransCanada would carry roughly 800,000 barrels of oil a day from Alberta to refineries along the Texas Gulf Coast, passing through Indigenous territories in Montana, South Dakota, Nebraska, Kansas and Oklahoma.

While some vow to stop it, others want to ensure development doesn't trample Indigenous rights.

"This is an important moment to remind Canadians that First Nations hold inherent rights and treaty rights recognized in Canada's Constitution," reads a statement from Assembly of First Nations National Chief Perry Bellegarde, issued shortly after the pipeline's approval. 

"This includes the right to free, prior and informed consent over any activities that could affect our lands, our lives or our futures."

Fears for environment

The Assembly of First Nations recently wrapped up its second National Energy Forum in Ottawa, where the theme was "inclusive prosperity in our energy future" and where much of the discussion was about getting a seat at the development table.

Francois Paulette

Francois Paulette is against the construction of pipelines and has been campaigning against Keystone XL for years. (Pat Kane/CBC)

But in northern Alberta, the source of much of the oil the pipeline could carry, there's fear for what Keystone XL's approval means for the environment.

"It says to me they're going to pollute the rivers," said Francois Paulette, a Dene elder and environmental activist from Smith's Landing First Nation. "Have a bigger impact on the air, the rivers we live along down the Mackenzie River."

"That's where the biggest impact will be felt by the Indigenous people."

Fight 'begins anew'

Keystone XL has faced multiple delays since it was first pitched in 2008. When it was blocked by President Barack Obama in 2015, many environmentalists declared a victory.

Now, south of the U.S. border, many Indigenous groups are vowing to fight once again.

"The fight to kill the Keystone XL pipeline begins anew — and Donald Trump should expect far greater resistance than ever before," wrote Dallas Goldtooth, lead organizer for the Indigenous Environmental Network.

"We've stopped the toxic Keystone XL pipeline once and we will do it again."

Keystone XL map March 2017

The Keystone XL pipeline would bring oil from Hardisty, Alta., to Steele City, Neb. (Natalie Holdway/CBC)

The Standing Rock Sioux tribe, which for months has been fighting the $3.8-billion US Dakota Access pipeline, announced its opposition to Keystone XL.as well.

"Once again, the treaty lands of the Great Sioux Nation are threatened by Keystone — a perilous pipeline," said tribal chair Dave Archambault II in a statement.

"We hope that everyone around the world who stood with Standing Rock on [the Dakota Access pipeline] will continue to stand with us and all the tribes as we continue to fight these dangerous and short-sighted infrastructure projects that serve only the interests of billionaires."

'Good neighbour'

TransCanada issued a news release on Friday stating that the company would continue to work with key stakeholders throughout Nebraska, Montana and South Dakota to obtain the necessary permits and approvals to advance the project to construction.

However, there was no mention of Indigenous communities in that press release, though the company's website does have a section called Community, Aboriginal and Native American Relations, which states that "TransCanada is committed to being a good neighbour and to building and maintaining positive relationships with the people who reside near our facilities and pipeline right-of-ways."

CBC News asked the company whether it has a specific strategy for dealing with Indigenous groups who oppose the Keystone Xl pipeline but received no response.

With files from Alex Brockman