By Phil Mercer
BBC News, Sydney
Environmentalists fear oil is heading towards an area where whales breed
A second attempt to stop oil pouring into Australian waters after a rig accident in the Timor Sea has failed.
It is almost two months since oil began flowing from the West Atlas drilling platform that lies about 200km (125 miles) off the West Australian coast.
The rig's operators have said that plugging the leak is an "extraordinarily complex" task.
Environmental groups have warned that the slick is threatening wildlife, including endangered turtles.
Conservationists have said this is Australia's most damaging oil spill in 25 years.
Each day for almost two months, hundreds of barrels have been flowing into the Timor Sea, although officials have conceded that it is impossible to know just how much oil has been spilt.
The slick is about 160km from the Western Australian mainland, and slightly further from the Indonesian coast.
Two attempts to plug the leak have failed.
Engineers have tried to cap a small hole 25cm wide that lies deep beneath the seabed.
They are expected to have another go towards the end of the week.
Scott Ludlam, a Senator for the Australian Greens, says it is a complex task.
"It underlines the extraordinary difficulty that they are facing in plugging the well," he said of the latest failure.
"They are trying to hit a needle in a haystack 2.5km below sea level. So, it is not surprising, I suppose, that they've failed to plug the well on their second attempt.
"This is the worst oil spill in Australian waters since the mid-1980s and it really does not give us high hopes for the huge expansion of the oil and gas industry that is planned in the region," he added.
The Australian Maritime Safety Authority has said the flow of oil from the damaged well appears to be slowing.
Boats have been spraying chemicals to help disperse the slick and stop it spreading.
A spokeswoman has insisted that the impact on wildlife had been minimal.
Environmentalists, however, worry about the long-term effects of contamination on vulnerable marine species, including flat-back turtles, dolphins and whales.