Oil and gas has been leaking from a faulty cement well on the West Atlas rig, about 250km off the far north Kimberley coast, since last Friday.
Despite assurances from the Federal Government and the rig's operator, PTTEP, that the slick is drifting away from the coast, a whale and her calf have been spotted alongside oil on the shore side of the rig.
Greens senator Rachel Siewert has flown over the rig and says she saw the whales near a breakaway slick. Strong ocean currents and wind are thought to have moved the slick towards land.
"There is a lot of oil that has spread substantially,'' Ms Siewert said.
"The Government have said that there is no risk to the coast, but that is nonsense. If it keeps flowing for the next seven to eight weeks, it is inevitable that oil will come ashore.''
It is expected to take seven-weeks to stem the flow of hydrocarbons forming a film of oil stretching over 180km from east to west of the rig.
The Government-run Australian Maritime Safety Authority, which is managing the clean-up, has labelled it one of the worst spills to affect the WA coast.
Ms Siewert said legal action against PTTEP could not be ruled out.
Biologists say an endangered flatback turtle fitted with a tracking devise as part of a Barrow Island research project is on a collision course with the toxic slick.
Since late November, the 20-year-old female turtle has travelled 914km along the west coast.
The Wilderness Society says the Kimberley coastline is a "marine superhighway'' used by 19 species of whales and dolphins, sea snakes, birds and fish.
WWF marine biologist Ghislaine Llewellyn says the tracking devise on the turtle illustrates the impact a disaster of this scale can have on a range of marine life.
Ms Siewert has accused the Government and PTTEP of misleading the public on the size and extent of the spill.
PTTEP says it will take at least seven weeks to stop the flow of oil because it needs to tow in another rig from Singapore.
Conservation groups have called on PTTEP to use a rig offered by Woodside Petroleum, which is only five days away.
PTTEP refused and a spokesman would not comment on the company's refusal.