Swimmers and surfers were Tuesday warned to steer clear of beaches in parts of eastern Australia after four shark attacks in the space of 48 hours.
Heavy rains stirring up murky waters have been blamed for the unusual spate of attacks in the state of New South Wales.
Surf Life Saving New South Wales said the turbid waters were ideal for bull sharks, urging people to stick to the pool until conditions cleared.
"We have such poor water quality that's conducive to bull shark activity," the water safety body told national broadcaster ABC.
"Just go to a local pool, because at this stage, we're advising that the beaches are unsafe."
A surfer on the state's Mid North Coast was lucky to escape with "minor" injuries after he was bitten by a shark while catching waves Tuesday, Surf Life Saving New South Wales said.
It was the state's fourth recorded shark attack over the past 48 hours.
In one of those attacks, a shark bit a man's legs as he surfed at Manly, leaving him in a critical condition.
A few hours earlier, an 11-year-old boy escaped uninjured when a shark took a bite out his surfboard a little further north.
All of Sydney's northern beaches have been closed until further notice.
On Jan. 18 afternoon, a 12-year-old boy was seriously injured as he swam at a beach on Sydney Harbor.
Scientists suggested recent heavy rain had attracted bull sharks to coastal areas where rivers emptied into the sea.
