Great white shark halts Backstairs Passage swim

Kangaroo Island marathon swimmers Shane Sanigar and Jakob Zeman almost realised their dream of swimming across Backstairs Passage on Tuesday.

But their epic swim was called off with less than 2 kilometres to go after a four meter great white shark having a close look at them.

Shane said they were swimming together when Jakob screamed "Shark".

The shark came within a few metres of the swimmers, before they called the boat back and hopped on board.

"We had a good at go at it and now we will contemplate the future," he said.

The support boat left Penneshaw on Tuesday, April 16 at first light crossing the passage in calm conditions, arriving Cape Jervis at about 7.30am.

The pair jumped into the water and started the 17.4-kilometre swim back to Kangaroo Island.

In the support boat is KI local Dave Clark, who said everything was going well and the two boys were in the water and swimming strongly.

"Everything is going well and conditions are perfect," Dave reported at 10.30am.

They are equipped with two electronic shark deterring devices, one on loan from WA company and the other provided by local tour operator Tony Coppins.

The swimmers were well ahead of schedule to reach Penneshaw around mid afternoon and called off the swim just after 12noon.

With only three to four kilometres to go they were heading for Snapper Point because of the tide.

This was the third attempt with two previous swims called off before even starting due to poor weather conditions, most recently on Sunday, April 14.

But the biggest challenge is always getting across before the next tide begins.

Shane has decided to donate money raised from the swim to the Australian Cancer Research Foundation and donations can be made at his ACRF page.