Investigators say at least one million litres of petroleum crude oil were released when a freight train derailed last month on a ranch in western Manitoba.
The update from the Transportation Safety Board on Friday was the first indication of how big the Feb. 16 spill was near the small community of St. Lazare.
"The TSB work on site has been completed," the safety board said in a news release.
"All 35 of the damaged tank cars were examined and seven of them were selected for a more detailed examination to be conducted at a later date ... to evaluate tank car performance.
"The TSB has also recovered select track components and wheel sets ... which are being forwarded to its engineering laboratory in Ottawa for detailed failure analysis."
The Canadian National train, with 110 petroleum crude oil cars, was heading east in the early morning at an estimated 79 km/h when an emergency brake was applied, the agency said.
It said 37 cars derailed and 16 cars ruptured. The spill was mostly contained in a low-lying area adjacent to the track.
There were no injuries and no fire. No residents in the area had to leave their homes.
The board rejected an interview request Friday and said it was too early to comment on the extent of any environmental impact.
Barry Lowes, reeve of the Rural Municipality of Ellice-Archie that includes the site, said cold weather helped responders contain the spill quickly.
"The ground was all froze, the little pond that it fell into was froze right through, so the impact isn't as large as it would have been at a different time of the year," Lowes said.
Still, he said, residents have concerns about the increasing number of trains going through the area and are hoping to get more information on the derailment in upcoming discussions with CN.
"There's lots of (trains) going through that are carrying oil — way more than there used to be, so of course we're concerned."
Jayme Corr, who raises cattle on almost 1,000 hectares of land that includes the spill site, said CN was still moving dirt, ice and pond sediment on Friday.
"I think they're doing all they can do. I'm just going to hold them accountable to get it cleaned up."