A celebration erupted at the main protest camp in Cannon Ball, North Dakota, where the Standing Rock Sioux tribe and others have been protesting against the 1,172-mile (1,885km) Dakota Access Pipeline.
The US Army Corps of Engineers said on Sunday that it had turned down a permit for a controversial oil pipeline project running through North Dakota, in a victory for Native Americans and climate activists who have protested against the project for months.
"The Army will not grant an easement to cross Lake Oahe at the proposed location based on the current record," a statement from the army said.
Protesters have said the $3.8bn project could contaminate the water supply and damage sacred tribal lands.
"I hope they follow through here with this. They haven't been following the law all along. So we'll see - but this is a victory today for our people and our water," said Native American Gerad Kipp, 44, an irrigation engineer from Missoula, Montana.
Standing Rock Chairman Dave Archambault II thanked activists for their support in the protest effort.