A Native American tribe in South Dakota is on edge following a large oil leak from TransCanada's Keystone pipeline.

TransCanada said in a statement Thursday 795,000 litres of oil leaked from an underground section of its Keystone pipeline near Amherst, S.D., about 64 kilometres west from the Sisseton Wahpeton Oyate of the Lake Traverse Reservation.

Sisseton Wahpeton Oyate tribal chairman David Flute said his community is concerned the leak, the largest by the Keystone pipeline in South Dakota to date, could pollute the area's aquifer and waterways.

"We are keeping a watchful eye and an open ear," said Flute.

"The concern is at a high level, but there is really nothing we can do."

Sisseton-Wahpeton Oyate Tribal Chairman David Flute

Sisseton Wahpeton Oyate Tribal Chairman David Flute says there is a high level of concern on his reservation following a Keystone pipeline spill in South Dakota. (YouTube image)

The spill comes at a sensitive time for TransCanada, which is facing a vote by the Nebraska Public Service Commission Nov. 20 on whether to accept TransCanada's Keystone XL proposal.

TransCanada is seeking to shorten the Alberta crude's transport route from Hardisty, Alta., by laying new pipeline through Montana, South Dakota and Nebraska where it would meet existing infrastructure in Steele City, Kan., and on to the Gulf Coast.

Keystone XL facing opposition

Keystone XL has faced stiff opposition from Nebraska landowners and Native American tribes.

Dallas Goldtooth, with the Indigenous Environmental Network, said there are 15 tribal nations along the Keystone XL route.

"It poses a risk to the Indigenous rights of tribal nations all along the route and it's a complete disregard for free prior and informed consent as guaranteed on the UN Declaration on the Rights of Indigenous Peoples," said Goldtooth, who is directly involved in campaigns against the pipeline's construction.

"It puts at risk the drinking water of over 65,000 Indigenous peoples along the route and puts at risk the livelihood for so many people that depend on tourism, on the land itself for farming and livestock. It's a risk we can't take."

Goldtooth was also involved in the Standing Rock Sioux tribe's battle over the Dakota Access Pipeline which unfolded roughly 350 km west of the Amherst spill.

Concern over time lag in notice

Brian Walsh, an environmental manager with the South Dakota Department of Environment and Natural Resources, said one of his officials was at the scene of the rupture and noticed some crude leaching to the surface. He said the majority of the spilled crude remained underground.

Walsh said the spill site does not sit over any mapped shallow aquifers and there were no major waterways or residential wells in the immediate vicinity.

"It is possible there is shallow groundwater at the site," he said.

Dallas Goldtooth

Dallas Goldtooth, with the Indigenous Environmental Network, has been campaigning against the Keystone XL proposed pipeline project. (Courtesy of REDx)

Walsh said this is the largest leak by the Keystone pipeline in South Dakota. He also said the pipeline spilled about 64,000 litres in April 2016 near Freeman, S.D., about 300 km south of the Amherst spill.

"At at this point we don't know what caused it," he said.

TransCanada said in a statement it noticed a drop in the Keystone pipeline's pressure at about 6 a.m. local time. Walsh said the state was alerted at 10:30 a.m. local time.

"We will certainly be looking into the time difference between when they knew and when we knew," he said.

Wind power also a threat

Flute said the Sisseton Wahpeton Oyate tribe was notified at about noon local time. He said he would also be looking into the time lag between when the company discovered the spill and when the tribe was alerted.

Flute said he expects the spill will have environmental impact.

"We are in a heavy migratory route here with a lot of waterfowl and upland game," he said.

"There is going to be a concern with any type of fossil fuels that are being transported … any type of disturbance to the earth and, especially, the water."

He said Native Americans have been concerned about the impacts of pollution since the advent of the Industrial age, but the world runs still runs on oil.

"As Indigenous people we use fossil fuels too. We drive cars, tractors, motorcycles, boats and lawnmowers," he said.

But even green energy poses a risk in his territory, he said.

"In my reservation we are right directly in the middle of the Midwest migratory route, it's big, that comes from Canada," he said.

"There is some concerns with the wind power that are going up, too."