The U.S. Army Corps of Engineers has halted the construction of the Dakota Access Oil Pipeline.
The decision is a major victory for the Standing Rock Sioux tribe and the several thousand protestors that have been camped out near the site for many months.
The proposed pipeline would run near their reservation and underneath the Missouri River.
Opponents say it threatens the water supply of several million people in the Midwest and that it violates treaties between the federal government and the Sioux Nation.
The pipeline is largely complete except for the now-blocked segment.
The Army Corps says alternate routes will be examined.