The Dakota Access oil pipeline faces new uncertainty after the Army Corps of Engineers said Friday that a court-ordered environmental review won't be completed this year and will extend through next spring.

"The Corps' original estimate that its review and analysis of the remand issues would conclude between late November and early December 2017 was based in part upon the Corps' understanding that it would take Dakota Access approximately 30 days to provide the requested information," federal lawyers said in a court brief filed Friday.

The Army Corps is waiting on the company's oil spill modeling to inform its review of the leg of the 1,100-mile pipeline that goes underneath Lake Oahe in North Dakota.

The pipeline has become a focal point for anti-fossil fuel activists who oppose oil drilling and fracking while prompting fears from Native American groups that the pipeline poses a risk of an oil spill at one of the only sources of fresh water in the region.

President Trump has made approval of the Dakota Access pipeline a key piece of his energy agenda. He signed an executive order early in his presidency to expedite its approval.

The district court judge who ordered the new environmental review did so in response to litigation from tribal groups. The judge is allowing oil to continue to flow through the pipeline while he decides whether to shut it down until the Army Corps completes its review process.