Andrew LaMacchia said he had not seen anything like it in decades of fishing on the South Coast.

The 12m whale appeared yesterday morning off Wollongong Harbour, not far from the shipping lanes at Port Kembla.

It had rolled over on to its back with its fins outstretched.

As it has decomposed, the whale's abdomen has bloated until it reached about three metres above the waves in a huge dome.

There were no obvious wounds on the whale's body, so it was not immediately known how it had died.

Water police were called in around lunchtime to tow the whale away from the shipping lane, but when they arrived they discovered it had already floated out of the area.

Yesterday afternoon, currents had taken the whale south to Port Kembla and it was continuing in a southerly direction.