A US federal judge has declined to temporarily halt construction of the final section of the controversial Dakota Access oil pipeline.
US district judge James Boasberg's decision, which comes a week after he held a hearing to consider the matter, means the pipeline could be in operation this month.
Native American tribes the Standing Rock and Cheyenne River Sioux had asked Judge Boasberg to direct the US Army Corps of Engineers to withdraw permission for Texas-based developer Energy Transfer Partners to lay pipe under Lake Oahe in North Dakota.
The stretch under the Missouri River reservoir is the last piece of construction for the 3.8 billion dollar (£3 billion) pipeline to move North Dakota oil to Illinois.
The ruling is not the end of the court battle, as no final decision has been made on the merits of the tribes' claims that the pipeline threatens cultural sites, water and religion.
Meanwhile, Native Americans from across the US are holding a protest in Washington DC against the Trump administration and its approval of the pipeline.
The demo in the US capital kicks off four days of activities which will culminate in a march on the White House.
Tribal members and supporters plan to camp each day on the National Mall, with teepees, a ceremonial fire, cultural workshops and a number of speakers planned.
Native American leaders also plan to lobby politicians to protect tribal rights.
Dave Archambault, the chairman of the Standing Rock Sioux tribe, said: "We are calling on all our Native relatives and allies to rise with us.
"We must march against injustice. Native nations cannot continue to be pushed aside to benefit corporate interests and government whim."
On Friday, the two-mile "Native Nations March on DC" will lead participants from the Army Corps of Engineers office to a rally near the White House.
Organisers have not released an estimate on how many people or tribes planned to take part.
The White House has not responded to a request for comment.
The march on Friday will begin at the Army Corps of Engineers office because the agency manages the Missouri River and last month gave the pipeline developer, Texas-based Energy Transfer Partners, permission to finish the project. The company expects to wrap up the work and have oil flowing this month.
The two tribes feel they were not properly consulted about the pipeline route, which the government disputes.
They also maintain their treaty rights were violated when the government changed its mind about conducting further environmental studies of the Lake Oahe crossing after President Donald Trump took office in January.
Dallas Goldtooth, an organiser with the Indigenous Environmental Network, said: "This fight against the Dakota Access pipeline has been the tip of the spear of a powerful global movement calling for the United States government and Donald Trump to respect indigenous nations and people in our right to water, land, sovereignty and culture."