The Dakota Access Pipeline isn't fully open for business, but it's already suffered a minor oil spill.

Early last month the controversial pipeline leaked roughly 84 gallons of crude oil in South Dakota.

The spill occurred at a rural pump station and didn't pose a threat to the public's drinking water, local authorities said.

"It was immediately contained and cleaned up," said Brian Walsh, an environmental scientist at South Dakota's Department of Environment and Natural Resources.

Walsh called the spill "relatively small" and said that while it was the first for Dakota Access in the state, such spills are not uncommon.

He said the incident was caused by a mechanical failure and mitigated by a liner that provides secondary containment.

The April 4 spill was disclosed on the agency's website, but it gained little attention until The Associated Press reported on it on Wednesday.

Energy Transfer Partners, the pipeline's developer, confirmed the incident in a statement, saying there was "no impact to the area" and "all remediation" was completed shortly after it occurred.

Related: Oil stocks are the biggest losers of 2017

The spill is sure to give more ammo to the vocal critics of Dakota Access, a 1,172-mile long pipeline. Its construction has been strongly opposed by Native Americans and environmentalists. Despite protests, in January the Trump administration advanced the $3.7 billion pipeline in an effort to create jobs and enhance America's energy security.

"This just proves their hastiness is fueled by greed not in the best interest for tribes or the Dakotas," Joye Braun, a member of the Cheyenne River Sioux, said in a statement put out by Indigenous Environmental Network, a nonprofit that has opposed Dakota Access.

"Do we have more spills just waiting to happen? This is our home, our land and our water," Braun said.

The Standing Rock Sioux Tribe continues to fight Energy Transfer Partners (ETP) in court in an effort to halt the project's expected opening next month.

"This is what we have said all along: oil pipelines leak and spill," Standing Rock Chairman Dave Archambault II said in a statement about the incident.

Archambault argued that the court must halt the project to protect the tribe as well as the "17 million people whose drinking water is at risk."

Once it's operational, Dakota Access is expected to move nearly half a million barrels of crude oil each day across the Midwest.

In March, the company said Dakota Access has been vandalized in several places as part of "coordinated physical attacks."