PORTLAND — Emergency personnel are on the scene of a heating oil spill at the Portland International Jetport.

The oil has reached the Fore River near the end of Yellowbird Lane, according to state Department of Environmental Protection officials. The amount of oil spilled is believed to be 600 gallons or less.

A sheen on the water was reported just before noon. The Coast Guard is deploying absorbent booms to try to keep the spill from spreading.

Portland officials say the cause of the spill was a malfunction in the jetport’s heating system.

An automatic pump that sends No. 2 heating oil through the system continued to pump after it was supposed to stop, officials say.

They say the accumulating oil traveled up the vent system and onto the roof of the jetport’s new terminal, where it entered the storm drain system and traveled out to the Fore River.

A strong odor of oil was permeating the new terminal and the east end of the Jetport this afternoon.

Clean Harbors is on the scene to clean up the spilled oil. Portland firefighters also responded to the scene.

The No. 2 fuel oil came from a 600-gallon day tank and was released when the malfunctioning pump failed to shut off when it was supposed to.

The fuel followed the stom drain to a retention pond, where some of it was contained and is being cleaned up. However, today’s rainy conditions helped push the fuel past the pond and into a cove of the Fore River. The Coast Guard, DEP, Portland Fire Department, jetport staff and Clean Harbors are using absorbent booms to keep the fuel from spreading into Long Creek or over to Thompson Point Marsh.

Officials said the situation is still evolving and that a higher than usual tide would be coming in after the 4:40 p.m. low tide because the moon is almost full. They planned to be on scene for at least 24 hours working to protect sensitive areas and clean up the spill.

A Department of Inland Fisheries and Wildlife biologist will determine whether the population of ducks in the area has been affected.