The Army Corps of Engineers on Sunday announced that it would deny the final permits necessary to continue construction of the controversial Dakota Access Pipeline.

After months of protests that have at times become violent, the Army Corps of Engineers said it would conduct and environmental impact study to seek alternative routes for the 1,170-mile pipeline.

“Although we have had continuing discussion and exchanges of new information with the Standing Rock Sioux and Dakota Access, it’s clear that there’s more work to do,” Army Assistant Secretary for Civil Works Jo-Ellen Darcy said in a statement. “The best way to complete that work responsibly and expeditiously is to explore alternate routes for the pipeline crossing.”

The Standing Rock Sioux tribe objects to the current planned route, saying it endangers their water supply and sacred lands. Thousands of Native Americans, veterans and others — including at least one local celebrity — have joined months-long protests and clashed with law enforcement.

The future of the pipeline remains uncertain, as President-elect Donald Trump has previously said he supports the pipeline and would grant the necessary permits.