FREDERICTON -- NB Power says about 3,000 litres of oil leaked into the St. John River after a seal on an underwater turbine hub at the Mactaquac Generating Station broke.

The Crown utility company says crews are working to repair the seal, which began releasing the oil late Friday morning.

The company says the leak involved Teresso 32 lubricating oil, which is not expected to be harmful to aquatic organisms and is biodegradable.

But Keith Cronkhite, vice-president of generation and business development for NB Power, says given the type of material released and the high river flows at the time of the incident, the company is advising the public of the spill as a precaution.

NB Power says staff were alerted to a possible problem by an alarm in the station's fourth turbine and they shut down the unit to prevent more oil being released.

The company says the leak was immediately reported to federal and provincial environmental authorities and a licensed cleanup contractor was called to the station.

It says fast-moving spring river flows quickly moved the oil downstream, making it impossible for cleanup crews to collect and remove the material.