Dramatic scenes at the annual Rottnest Swim as scores of swimmers were pulled from the water after a shark sighting.
The shark was seen at the 12 km mark of the swim, just over half way. Swimmers swimming in the vicinity of the mark were asked to go back to their boat and either return to Perth or continue to Rottnest immediately.
The shark is reportedly 3.5 m long.
Swimmers further from this mark were allowed to continue onwards, but were asked to remain vigilant and wary of any radio warnings.
Other swimmers approaching the mark were pulled from the water and asked to stay with the boat until the shark had cleared.
The shark warning was issued just after 1015 this morning and swimmers were allowed to continue 45 later.
No shark attack has been reported as of yet.
It had already been an eventful day for event organisers, with a support boat capsizing just after 9am, only hours from beginning the swim. The call from the radio sounded "ah, sea rescue, this is Aurora. She's going fast".
Over two thousand swimmers participate in the event each year.