Law enforcement officials say construction has resumed on the four-state Dakota Access pipeline on private land in southern North Dakota.
Crews dug trenches and laid pipe in the St. Anthony area.
A federal appeals court ruling Sunday cleared the way for work to resume on that land.
The work on federal land is still on hold.
The Standing Rock Sioux Tribe opposes the pipeline over concerns about drinking water and cultural sites.
Thousands of people have protested and 123 people have been arrested since mid-August, including actress Shailene Woodley and Green Party presidential candidate Jill Stein.
Woodley livestreamed her arrest Monday on social media and the video of what appeared to be a peaceful protest has been viewed three million times.
Cass County Sheriff Paul Laney, who was assisting law enforcement at the protest, called it a riot.