An American documentarian arrested while filming an oil pipeline protest in North Dakota says she was “dumbfounded” by her three counts of felony charges, which could see her in jail for 45 years.

Deia Schlosberg, the producer of the upcoming documentary “How to Let Go of the World and Love All Things Climate Can’t Change,” was arrested at a TransCanada Corp's Keystone Pipeline site in Pembina County on October 11.

Schlosberg was taken into custody while filming activist Michael Foster as he shut off a valve of the Canadian tar sands pipeline.

Authorities confiscated Schlosberg’s equipment and footage from the protest. She has been charged with conspiracy to theft of property, conspiracy to theft of services and conspiracy to tampering with or damaging a public service.

The three felony charges together carry a maximum penalty of 45 years behind bars.

“From the beginning, I was just dumbfounded by the charges,” Schlosberg told Russia Today in an interview on Tuesday. “They seem to come from out of nowhere.”

“I was doing my job,” she said. “I was documenting a climate action."

“I was documenting and they didn't know what my involvement was. I told them I was a filmmaker and that I was filming from public property, and they still put me in jail for 53 hours and (charged) me with three counts of conspiracy, which are all felonies.”

Josh Fox, an Oscar-nominated director who has co-produced the documentary with Schlosberg, said in an open letter to President Barack Obama and North Dakota Governor Jack Dalrymple that the charges against his colleague were "unfair, unjust and illegal."

"Journalism, especially documentary filmmaking, is not a crime, it's a responsibility. The freedom of the press is a fundamental right in our free society. The charges filed against her are an injustice that must be dropped immediately," said the letter, which was signed by more than 30 artists, filmmakers, writers and journalists.

The 1,100-mile (1,770-km) pipeline would be the first to transport crude oil from Bakken shale, a vast oil formation in North Dakota, to refineries in the US Gulf Coast.

This file photo taken on September 3, 2016 shows members of the Standing Rock Sioux Tribe and their supporters opposed to the Dakota Access Pipeline (DAPL) confront bulldozers working on the new oil pipeline. (Photo by AFP)

Members of the Standing Rock Sioux Tribe have been protesting to block the $3.78 billion project for months.

In the latest escalation of tensions on Saturday, at least 127 protesters were arrested during a peaceful gathering near the site of the controversial pipeline after police tried to disperse them using pepper spray.

Tribal leaders slammed the disproportionate and unnecessary show of force by local police, and called on the US Justice Department to intervene on their behalf.

Last month, bulldozers destroyed sacred tribal sites whose locations had been identified in court documents.