Indigenous people from across North America are joining the White House protest against TransCanada's proposed Keystone XL pipeline, which would carry crude oil from northern Alberta to Gulf Coast refineries in Texas.

Several First Nations leaders from Canada are making the trip to join the protest Sept. 2.

Protesters have gathered outside the White House in Washington, D.C. since Aug. 20, with actors and scientists among those opposing the pipeline. Over 250 people have been arrested, including Canadian actors Margot Kidder and Fort McMurray, Alta.,-born Tantoo Cardinal.

The Indigenous Environmental Network is organizing the effort to bring indigenous people to the U.S. capital. Campaign organizer Clayton Thomas-Muller said they've seen a "tremendous" outpouring of support from across North America and Europe for local people in Northern Alberta.

George Poitras, former chief of the Mikisew Cree in northern Alberta, plans to join the protest. He believes the oil sands have already had a dire impact on people's health in his community of Fort Chipewyan.

"We would like President Obama to hear our pleas; perhaps he will not approve this pipeline," he said.

Chief concerned about water quality

Bill Erasmus, Regional Chief with the Assembly of First Nations in the Northwest Territories, plans to attend and has already written a letter protesting the pipeline to U.S. Secretary of State Hillary Clinton.

Erasmus says he's concerned about water quality.

"Everything that happens in Alberta is part of the Mackenzie water basin, all that water comes north," he said.

The pipeline passed a major hurdle on Friday when the U.S. State Department said there was no significant risks to the six U.S. states it would cut through.

The assessment moved the administration of President Barack Obama a step closer to a final decision on the pipeline. It now has about three months to determine whether the controversial project is in the national interest of the United States.

Keystone XL has become a lightning rod for the environmental movement in the U.S. in the aftermath of failed climate-change legislation last year.

Proponents, meantime, say the pipeline will create thousands of jobs and help end U.S. reliance on Middle Eastern oil.

With files from The Canadian Press