A pipeline in northwestern Alberta has spilled about 100,000 litres of a mixture of water, oil and gas.

Calgary-based NuVista Energy owns the six-inch diameter oil emulsion pipeline, which leaked about 100 kilometres northwest of High Level, Alta.

On Friday afternoon, a helicopter crew doing regular daily inspection and maintenance work saw a "small area of stressed vegetation" along the pipeline route and the line was shut down immediately, NuVista said in a statement Wednesday.

"Safety and protecting the environment are top priority at NuVista Energy," said CEO Jonathan Wright. "Our staff train regularly for potential unexpected events. We responded within minutes as soon as we knew there was a problem."

NuVista said it was investigating what caused the leak.

The five-kilometre pipeline runs from an oil testing facility to an oil battery.

So far, there have been no reports of harm to wildlife. A two-metre-high fence has been put up to prevent animals from getting into the site.

NuVista said Alberta Energy Regulator investigators and First Nations officials inspected the property on Sunday.

The company said an initial survey indicates an area of about 110 metres by 120 metres has been affected.

Workers are laying down mats to allow heavy equipment into the remote site.

In June, a pipeline at Nexen's Long Lake oilsands site southeast of Fort McMurray, Alta., spilled about five million litres of bitumen, sand and produced water over a 16,000 square metre area.

Produced water is a term used by the industry to describe water produced as a byproduct along with oil and gas.