An eight-metre dead whale has been washed onto rocks at the mouth of the Clyde River in Batemans Bay.

Canberra visitor David Haberlah saw the whale on Saturday afternoon, just minutes before waves dumped the mammal in an area known as North Head beach, near Yellow Rock.

With his four-year-old daughter, Siwa, the geologist hurried to the scene.

"I was sitting at the far end and I saw something white floating," Mr Haberlah said. "I thought 'wow, this looks like a massive balloon'. I had a closer look and saw one of the fins come up and realised it was a whale.

"I went running back and Siwa and I went straight to look. It was belly up. It was already dead."