Fire crews were called out to tackle an oil tank on fire at Hatton waste water treatment works outside Arbroath in the early hours of Wednesday morning.
Scottish Fire and Rescue were called to the sewage plant at 2.22am.
They discovered an a large industrial unit – around 50 metres by 35 metres – containing an oil tank ablaze.
Four appliances attended the incident and firefighters wearing breathing apparatus used jet hosreels to bring the flames under control.
It took two and a half hours to get the blaze fully under control.
Investigators will return to the site later on Wedenesday to try to determine the cause of the fire.
