Fishermen spot hammerhead shark in Lake Illawarra

But on Saturday, Lake Illawarra had a visitor seldom seen there - a hammerhead shark.

Liam Shean and Jackson Valk were fishing from a boat on the lake, opposite Reddall Reserve between the entrance and Windang Bridge, when they saw something approaching.

"It looked like seaweed coming up to us," Mr Shean said.

But it was not seaweed; it was instead a hammerhead shark that Mr Shean estimated was between 1.5 and two metres in length.

Quickly the pair grabbed their phones and began filming the "one-of-a-kind" encounter.

Mr Shean, a lifelong Illawarra resident who lived opposite the lake, said he had never seen a shark there in his 21 years, although he knew someone had been bitten by one in its waters.

That was likely Steven Fogarty, who suffered puncture wounds to his leg when he was grabbed by what was believed to be a 1.5-metre bull shark as he snorkelled beneath the bridge in January 2009.

After he and Mr Valk saw the shark, Mr Shean said, it swam back towards the lake.

There are three species of hammerhead shark in NSW waters: the great hammerhead shark, the scalloped hammerhead shark, and the smooth hammerhead shark.

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The great hammerhead sharks is listed as a vulnerable species, while the scalloped hammerhead shark is endangered.

Hammerhead sharks are not considered dangerous to humans; the Australian Marine Conservation Society says there has never been a death attributed to a hammerhead shark in Australia.

Eleven hammerhead sharks were caught and died in shark nets off the Illawarra coast during the 2021-22 season, a recent Department of Primary Industries review revealed.

Hammerhead sharks are not among the 'target' species for the net program.