On Jan. 18, the U.S. Army began the process of opening an environmental study of the Dakota Access Pipeline crossing in North Dakota, a move that has been challenged by the company constructing the controversial project.

The Army said on Jan. 18 that it is gathering information to prepare an environmental impact statement regarding an easement to cross at Lake Oahe, a water source upstream from the Standing Rock Sioux Tribe's reservation that has been the focus of months of fierce protests due to fears the pipeline could damage drinking water and desecrate sacred grounds.

The U.S. Army Corps of Engineers in December denied Energy Transfer Partners an easement to drill under the lake.

The Army announcement comes as demonstrators renew opposition against the $3.8 billion project, with arrests this week bringing the total to more than 600, according to law enforcement.

Energy Transfer Partners, the operator, requested on Jan. 16 that a U.S. District Court judge for the District of Columbia stop the Corps of Engineers from initiating the environmental impact statement process until there is a ruling on whether the company already has necessary approvals for the pipeline crossing.

U.S. District Judge James Boasberg had scheduled a hearing in the case for the afternoon of Jan. 18.

In July 2015, the Corps granted Energy Transfer Partners permission for its proposed pipeline crossing at Lake Oahe.

For months, Native Americans and environmental activists have been protesting the pipeline, garnering support from celebrities and on social media.

Following the Army Corp's December announcement, the Standing Rock Sioux asked demonstrators to disperse and many did. However, some have remained.

On Jan. 16 and 17, 16 people were arrested for a number of offenses, including engaging in a riot and assault on a peace officer, bringing the total number of arrests to 603 since Aug. 10, which was around the time the protests began, according to Maxine Herr, a spokeswoman for the Morton County Sheriff's Department.

The department is hoping that President-elect Donald Trump will deploy federal help to law enforcement managing protesters.

"When Trump takes office, we foresee a significant change in terms of federal assistance," Herr said.

The North Dakota National Guard had deployed a missile defense system to the area near the protest site, but it was unarmed and being used only for observation purposes, said Amber Balken, a spokeswoman for the North Dakota National Guard.

The Avenger missile system had been in place for a "few weeks," but would be removed Jan. 18, Balken said.