The US army has notified congress that it will allow the controversial Dakota Access oil pipeline to cross under a Missouri River reservoir in North Dakota.
The move will complete a four-state project to move North Dakota oil to Illinois which has led to complaints from the Native American Standing Rock Sioux tribe that a leak in the pipeline could pollute drinking water.
The US justice department has filed court documents on the matter to members of congress from deputy assistant army secretary Paul Cramer.
The army intends to allow the crossing under Lake Oahe as early as Wednesday.
The crossing is the final big chunk of work on the 3.8 billion dollar (€3.5bn) pipeline.
The Standing Rock Sioux tribe has promised to continue with legal challenges against the move.
Dallas-based pipeline developer Energy Transfer Partners has insisted the pipeline is safe.