Backstairs Passage swim to Kangaroo Island underway

12.15PM: Called off with less than 2 kilometres to go due to a four meter great white shark having a close look at them.

11.15AM: Only three to four kilometres to go! They are heading for Snapper Point because of the tide.

10.42AM: Dave reports the boys are two-thirds of the way across and making excellent time!

10.30AM: Dave Clark in the support boat says everything is going well and conditions were "perfect".

9AM: Kangaroo Island marathon swimmer Shane Sanigar and his young swimming partner Jakob Zeman have started their swim across Backstairs Passage.

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.

They jumped into the war 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.

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 are hoping to reach Penneshaw around mid afternoon if everything goes well.

This is the third attempt with two previous swims called off due to poor weather conditions most recently on Sunday, April 14, but the biggest challenge will be getting across before the next tide begins.

Stay tuned for more updates during the day.

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