The Royal Canadian Navy is investigating a "very rare" fuel spill in Halifax Harbour last week that saw about 800 litres of fuel overflow from a tank on HMCS Athabaskan.

The incident happened Friday while the Athabaskan — the flagship vessel in the navy's East Coast fleet — was being fuelled up by HMCS Preserver at the Halifax Dockyard.

"Because we fuel all the time, this is a very rare circumstance that we have a fuel spill," said Commodore Craig Baines. As commander of Canadian Fleet Atlantic, Baines is responsible for the operation of the warships and support vessels.

"Because it's rare, I've basically implemented an investigation to determine exactly what went wrong," he said. "We take these issues very, very seriously because it obviously impacts our operations."

Saved by the boom

During the fill-up, the crew members realized they weren't getting the right reading on a sensor. 

"One tank was filling more than they expected and so they immediately took actions to shut the fuel off," said Baines.

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Commodore Craig Baines said the navy takes spills seriously, even if it's a minor incident. (The Canadian Press)

Of the 800 litres of fuel that leaked, the navy estimates up to 95 per cent was captured by the boom around the ship. About 40 litres went uncaptured, Baines said. 

"We had our ship's boats out in the water with soaker pads to clean up as much as possible," he said. Baines said Tuesday that work was completed.

Crews caught the spill quickly and "very well trained" teams worked on the cleanup, he said, adding the entire process took a matter of hours.

Baines said the navy considers this spill a minor one because most of it was contained. 

Not the first fuel leak

In an email to CBC News, Environment and Climate Change Canada said it had been told of the incident and "stands ready to provide scientific advice and support to the Canadian Coast Guard should it be required."

Baines said federal officials reacted quickly on Friday to help.

The navy says the investigation will determine whether it was a human or mechanical error — or both — that caused the spill from the Athabaskan. A probe will also help prevent similar situations from reoccurring, Baines said.

"We consider ourselves real stewards of the environment and it's important to us to get that right," he said.

It's not the first time a navy vessel has leaked fuel into Halifax Harbour. In 2011, the Preserver leaked 14,000 litres of fuel after an improper seal allowed fuel to seep into a pipe that passed inside a fuel tank and connected to the outside of the hull.