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Image courtesy of TransCanada/Twitter.

Flows through part of the Keystone pipeline were halted on Monday after a leak was discovered along the pipeline’s route in South Dakota.

According to the Argus Leader, the spill was first discovered on Saturday by a landowner near Freeman, South Dakota.

TransCanada said on Monday that emergency crews found “visible signs of oil on [a] small surface area” and are “safely excavating soil” for analysis.

Cleanup efforts were underway on Monday night.

The Calgary-based company said its crew and experts will continue assessing the incident.

The size and cause of the spill are still being investigated.

The portion of the Keystone line that moves oil from Alberta, Canada to Cushing, Oklahoma will be shutdown until at least Friday, CNN Money said.

The section of the line that connects Cushing to the pipeline’s section in Texas is still operating.

The U.S. Department of Transportation’s Pipeline and Hazardous Materials Administration told CNNMoney that it’s investigating the leak and has sent an inspector to the site.

The spill comes about five months after the Obama administration rejected the company’s Keystone XL project after a seven-year long review.

In January, TransCanada  filed a notice of intent to initiate a claim under Chapter 11 of the North American Free Trade Agreement (NAFTA) in response to the rejection.