Apache said more than 250,000 gallons of so-called produced water were released from its Zama production area in Alberta. The company said the fluid was mostly saltwater though it contained trace amounts of oil from extraction operations.
Oil operations in the region began in the 1950s. The Globe and Mail newspaper reported late Thursday the infrastructure associated with the release was 5 years old.
Tim Wall, outgoing president for Apache's operations in Canada, told the newspaper the company was puzzled by the incident.
"We just need to get this all cleaned up, get it reclaimed, do the remediation, then we'll figure out what happened," he said.
Aboriginal communities in the area said most of the trees in a 42 hectare site have died off. They said they suspect the release occurred during the winter, though Apache said it was confirmed last week.
"We'll go through a full investigation and we'll let people know [what happened]," Wall said.