A regulator in the US state of Nebraska has granted a final permit to build a contentious oil pipeline that has faced staunch opposition for years in both Canada and the US.

The Nebraska Public Service Commission approved construction on an alternative route for the Keystone XL pipeline on Monday morning local time.

Three commissioners voted in favour of the "mainline alternative route", and two voted against it.

Proposed by Canada-based energy giant TransCanada Corp, the nearly 1,900km pipeline could carry up to 830,000 barrels of oil each day from the Alberta tar sands to a terminal in Steele City, Nebraska.

The commission heard testimony earlier this year on the project, which has the support of US President Donald Trump but faces staunch opposition from local farmers and environmental and indigenous groups.

Its decision to grant the permit was based on whether the pipeline is in the best interests of Nebraska.

The commission could not take into account the risks of an oil spill since that issue is under federal jurisdiction and the pipeline already has an environmental permit.

'Legal question mark'

The commission did not take public statements during the brief public hearing on Monday.

The route that was approved on Monday runs east of TransCanada's preferred route, and "creates some uncertainty" because the company must contact landowners who will now be impacted, according to the Omaha World-Herald.

TransCanada will need to reach "property easement agreements with a new group of landowners," the newspaper reported.

"We will make sure that none of that route ever gets approved," said Jane Kleeb of Bold Nebraska, a local group that has been leading the fight against Keystone XL in Nebraska, after the vote.

Kleeb said the commission did not review the alternative route, and landowners along the alternative route were not consulted, which "throws the entire project into a huge legal question mark".

"We have to do everything we can in order to make sure that this pipeline never gets built," she said.

$8bn pipeline

Nonetheless, Trump approved a presidential permit for the $8bn pipeline last March.

The pipeline "represents a safe, reliable, and environmentally sound way to connect the American economy with an abundant North American energy resource produced by a neighbour that shares a commitment to a clean and healthy environment", TransCanada says on its website.

"The energy it carries will ultimately fuel the daily lives of Americans."

The company says the project will contribute approximately $3.4bn to the US GDP and create "thousands of well-paying jobs and substantial economic benefit to local communities".

From Nebraska, the oil will be diverted in two directions, towards Illinois and Texas, respectively.

Strong opposition

However, Nebraska landowners and environmental and indigenous activists have raised serious concerns about the project.

They say the risk of an oil spill is too great and would threaten local water supplies.

"It's definitely a risk," said Art Tanderup, a farmer and landowner in Neligh, Nebraska, whose land is along the proposed Keystone XL route.

Tanderup told Al Jazeera an oil spill would threaten the Ogallala aquifer, a vast underground water source that spans over 362,000sq km in the Great Plains region.

The aquifer feeds agriculture and other water needs in more than half a dozen US states, including Nebraska.

Monday's decision also comes only a few days after a leak in Keystone XL's sister pipeline, Keystone, spilled nearly 795,000 litres of oil in the nearby state of South Dakota.

"Why should TransCanada be allowed to build a new pipeline when one of their existing pipelines had a massive spill just last week?" said Greenpeace Tar Sands Campaigner Rachel Rye Butler in a statement after the Nebraska vote.

"It’s not a question of if there will be an oil spill from Keystone XL but when."

About 140 opponents of the project protested in the Nebraskan capital, Lincoln, on Sunday.

Amid slumping oil prices and difficulties getting its oil to foreign markets, TransCanada has said it will decide this month or in early December whether to build the pipeline, CBC News reported.

Tanderup said "there was no evidence that this is good for the state of Nebraska, absolutely no evidence at all".

Next steps

That was echoed by Commissioner Crystal Rhoades, who voted against the project on Monday.

She said TransCanada had not proven the construction of the pipeline would create "any positive economic impact for Nebraska".

She also said the company failed to consult indigenous communities that may be affected by the pipeline.

The Treaty Alliance, which represents indigenous communities along the Keystone XL pipeline route in both Canada and the US, said the Nebraska commission's decision "does not change a thing".

"People power will still stop this pipeline," the group said in a statement.

Indigenous tribes "up and down the Keystone XL pipeline route will be standing strong along with all our other allies to beat back this threat to our water, our people and our future," added Chairman Larry Wright Jr. of the Ponca Tribe in Nebraska.

Speaking to Al Jazeera before the vote, Tanderup said that even if the Nebraska commission granted the permit, Keystone XL opponents would continue to fight to stop the project from being built.

"We're going to continue to stand up to protect the water, to protect the land, to protect our indigenous relatives," he said.

"If it comes to it, we'll be standing there when the bulldozers come."