Aerial patrol general manager Harry Mitchell said warmer water would bring sharks closer to shore, and test flights and discussions with seafarers showed that sharks were already on the move this season.

"There is always activity there, especially as the whale migration south is still on and larger predators are out waiting for a big catch," Mr Mitchell said.

"We have seen a few in recent weeks. There were a few large ones around fishing boats last week."

Mr Mitchell said aerial patrol crews often saw great white, hammerhead, tiger and bull sharks during summer.

While sharks spotted this season had often been far offshore following schools of fish and fishing boats, Mr Mitchell said swimmers should remember what lurked off Illawarra beaches.

"We are already hearing of seal activity in Sydney and we get seals in Lake Illawarra, which are food sources for larger predators," he said.

"Right now, the sharks are no threat to the public. But we are around the corner from warmer ocean temperatures, and between December and March we will see an increase in marine life closer to shore."

The aerial patrol's Cessna 182 is undergoing major inspections, delaying the start of the patrol season.

Mr Mitchell said the familiar red and yellow planes would be flying over the Illawarra from late November.