The Australian Maritime Safety Authority (AMSA) has sent planes to investigate a substance resembling an oil slick in the ocean west of Darwin.
The authority does not believe the substance is related to a recent oil spill in the Timor Sea.
Yesterday AMSA sent planes to assess the clean-up of the leaking West Atlas oil and gas rig off Western Australia.
An AMSA spokeswoman says the oil slick has come within 170 kilometres of the Western Australian coast.
But aerial surveyors are also assessing a separate substance seen 120 kilometres west of Darwin that looks similar.
The area close to Darwin was filmed by an ABC camera crew.
While the maritime safety experts will further analyse the images, the authority remains confident the substance near Darwin is not related to the West Atlas oil leak.
The spokeswoman says oil leaking from the West Atlas rig would have dispersed naturally before it got anywhere near the Northern Territory coast.
She says the substance is also unlikely to be oil because it does not appear to have a sheen. Instead, it could be either coral spawn or an algal bloom.
An oil and gas industry expert has backed AMSA’s assessment, saying the substance is too far from the West Atlas spill to have originated there.
Moshtak Othman, who spent 13 years working as a petroleum resource manager for the Northern Territory Government, said it was hard to know what it might be.
“It can be anything; it can be misleading,” he said.
“It can be coral reefs. It can be natural leaks through the sea floor. It is historically proven that oil and gas can leak to the surface through cracks and fissures.
“Looking at the map, 120 kilometres west of Darwin, there are no operations, petroleum operations taking place at this time.
“There is no drilling, there is no production, so I would exclude very very much another oil spill or a spill or a kind of leak from any facilities.”