Coral on reefs north of Townsville must be checked for oil that has become stuck to coral, World Wildlife Fund's reef campaigners said on Monday.

WWF-Australia spokesman Richard Leck said reefs in low-lying coastal areas must now be checked after clean-up crews have begun to remove clumps of oil from beaches north of Townsville after oily film has drifted north.

Diving in The Great Barrier Reef. Credit:Tourism and Events Queensland

"If the spill drifted across reefs at low tide then it's almost certain there are now tar balls stuck to coral," Mr Leck said.

"It's possible to remove these sticky tar balls from reefs but if nothing is done they can take years to degrade," he said.