Police were told that three teenage boys, from Arcadia Vale, were spending their last day of the school holidays on the lake.

One of the boys told police that a shark leapt out of the water about 3.30pm while he was being towed on a surfboard behind a tinnie that his mate was driving.

Lake Macquarie Police Inspector Terry Burns said he would ask NSW Fisheries officers to investigate the incident.

He said police had examined the surfboard, which was missing a large chunk measuring 47 centimetres in diameter.

"If it's fair dinkum, you're talking a huge fish," he said.

The boy said one of his mates, who was in the boat, warned him that a shark was approaching.

The boy said he rolled off his surfboard and the shark bit into the board.

He said he swam several metres to the boat, before climbing in and watched the shark swim away.

The boy told his parents, who alerted police.

The Herald's historical records show shark attacks in the lake are rare.