Canadian regulators in Alberta said Canadian Natural Resource Ltd (USA) (NYSE:CNQ), the nation's largest oil producer, has been unable to stop leaks from a group of wells, the Wall Street Journal reported Friday.

There were four separate leaks first reported on May 20, resulting in about 175 barrels of crude oil spread over at least 100 acres near a Canadian Air Force base in northeastern Alberta, according to a provincial regulatory body.

"We don't know when they're going to get control of it," said Bob Curran, a spokesman with Alberta Energy Regulators.

Canadian Natural Resource said late Thursday that the "initial impacted area" was about 50 acres. It also attributed the leak to unspecified "mechanical failures of wellbores in the vicinity of the impacted areas."

The leak has not been a threat to people but has affected wildlife and vegetation. According to CNRL and the Alberta Environment Ministry 11 birds and small mammals such as beavers as well as 21 amphibians had been killed.