The US Army Corps of Engineers granted permission to complete the construction of the Dakota Access Pipeline, a major piece of infrastructure that had been embroiled in controversy and protests over the final remaining section which will run under a reservoir on the Missouri River.

On Tuesday the Army granted Energy Transfer Partners – the owner of the disputed pipeline – a 30-year easement under North Dakota’s Lake Oahe, which will allow the company to proceed along the previously contested route.

The easement is the final permit necessary to install the crude oil pipeline under federal lands currently managed by the Army Corps of Engineers and comes just weeks after President Trump signed an executive order directed toward completing the project under the premise that it "represents a substantial, multi-billion-dollar private investment in our Nation's energy infrastructure."

"Today's announcement will allow for the final step, which is granting of the easement," said acting Army Secretary Robert Speer. "Once that is done, we will have completed all the tasks in the Presidential Memorandum of January 24, 2017."

While the easement grants the company permission to finish the pipeline, a process that could be complete in a matter of months, opponents question its legality as it directly contradicts a previous decision by the Corps to halt construction until a proper environmental study was performed, which they began on January 18th.

Mr. Trump's memorandum, however, followed just six days later, prompting legal experts to question the legitimacy of the Corps' rapid change in position based on an executive order, according to the Associated Press.

The recent decision by the Corps represents a major setback to activists who had traveled from across the country and even internationally to gather in solidarity on the Standing Rock reservation to protest the construction of the $3.8 billion pipeline.

The Standing Rock Sioux Tribe, whose reservation sits less than a mile from the pipeline, sued the US Army Corps of Engineers back in July, seeking a preliminary injunction to stop the construction, partially due to the disruption of a sacred burial site by bulldozers working for the Dakota Access line.

Members of the tribe began protesting, arguing that the federal government had not adequately engaged local tribal leaders during the permitting process, as is legally required.

However, the protests snowballed dramatically, gathering widespread support from environmental activists fighting for the rights of the Standing Rock Sioux Tribe and to keep clean water sources unpolluted. Upset about the possibility that major water supplies could be contaminated should a leak or break occur in the pipeline – which is designed to move 470,000 barrels of oil each day, according to Time Magazine – the protests gathered nationwide support, with social media interest spreading internationally in a movement titled Stand with Standing Rock.

“We are a sovereign nation and we will fight to protect our water and sacred places from the brazen private interests trying to push this pipeline through to benefit a few wealthy Americans with financial ties to the Trump administration,” Standing Rock Tribal Council Chairman Dave Archambault II said in a statement on Tuesday, according to The Washington Post. “Americans have come together in support of the Tribe asking for a fair, balanced and lawful pipeline process. The environmental impact statement was wrongfully terminated. This pipeline was unfairly rerouted across our treaty lands. The Trump administration – yet again – is poised to set a precedent that defies the law and the will of Americans and our allies around the world.”

Further ignited by the occasionally violent interactions between protestors and local security forces, even some groups of US military veterans joined the protest, saying they wanted to protect the "water protectors" from alleged assault and intimidation.

Construction of the pipeline effectively came to a standstill when the Army Corps of Engineers announced on Dec. 4 that they would not grant the easement required to continue.

The project, initially proposed in 2014, would cross four states and deliver crude domestic oil from the rich basins of North Dakota to networks and refineries across the Midwest.

Proponents of the pipeline, including Trump, see such projects as instrumental to the further development of America's fossil fuel industry. The executive order underscored the president's stance that "construction and operation of lawfully permitted pipeline infrastructure serve the national interest."

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Energy Transfer Partners says that the pipeline is the safest, most environmentally sound and cost-effective method of crude oil transportation, which they say will further reduce America's dependence on foreign oil, according to CNN.

Since taking office, Trump has stated he would push to open up stalled infrastructure projects, such as the Dakota Access Pipeline and Keystone XL Pipeline – another controversial project, which has been stalled since the Obama administration denied permission for its construction in 2015.