KEY POINTS:
It was like a scene out of Jaws, as swimmers rushed from the ocean after sightings of a "monster" shark.
The drama happened yesterday morning at Sydney's La Perouse beach, just minutes before another alert just a few kilometres away at Bondi.
The world-famous stretch of sand was closed for 15 minutes - and around 150 people kept out of the water - after a distressed beachgoer told lifesavers he had seen a large shark.
At La Perouse in Botany Bay, the latest in a series of sightings of the "monster" shark - believed to be a great white - cleared the water of locals at the normally unpatrolled beach. Authorities are investigating residents' reports that a shark has taken a pet dog and a pelican in the area in recent weeks.
Brian Mangan, who runs the Boatshed Caf, said he spotted the shark chasing fish 200m from shore.
"It was quite a large shark, it would have probably been the size of the tinnies on the beach, or even bigger, and they're about 13 feet [4m]," he told smh.com.au.
"I could see the fin but I couldn't tell if it was a tiger shark or a white pointer, but it was big. It was making huge ripples, like a boat taking off."
The threat posed by sharks is a perennial summer talking point on Australia's busy city beaches, but a series of events have heightened this year's fears.
The remarkable escape by a diver who was half swallowed by a shark off Cape Howe in southern New South Wales last month made headlines around the world.
And last weekend 26-year-old Matt McIntosh lived to tell how he was dragged from his boogie-board by a shark near Ballina in northern New South Wales.
Surf Lifesaving Sydney spokesman Stephen Leahy said yesterday's reports had added to the public tension.
"People at La Perouse said it was a big shark - up to 15-feet long," he said.
"Many people, including some of our members, say this shark has been around for the last two weeks.
"Some of them think it was a white pointer but we can't be sure because it's very hard to identify a shark unless you're an expert."
After failing to find anything at Bondi, surf lifesavers re-opened the beach.
Leahy said higher numbers of sightings were common at this time of year because sharks were more active.
"We don't call them shark sightings, we call them shark alarms," he said.
"Quite often people see a large shape in the water and fear the worst. But it might be a dolphin or even a large clump of seaweed below the surface that creates a shadow."
Although Leahy said water lovers had nothing to fear, predicted rain could keep them away from the ocean over the next few days.
"There are some simple rules," he said. "People should not swim after rain because it brings debris and rubbish into the water which sharks find tasty."
