Swimmers were ordered from the water at Windang Beach yesterday after a 2m hammerhead shark was spotted 10m offshore.
Lifeguards closed the beach for an hour around 2pm after the hammerhead was seen feeding 20m north of the flags.
It was one of three shark sightings in Wollongong yesterday after a 3m hammerhead was also spotted 80m from Towradgi Beach and a shark was possibly seen near Stanwell Park.
Following the sightings, Bendigo Bank Aerial Patrol general manager Harry Mitchell issued a warning to swimmers.
"Don't swim or surf in murky water, particularly near estuarine areas," he said.
Sharks often loiter near estuaries to feed and are known to swim up inlets in search of food.
"A lot of our popular beaches up and down the coastline are adjacent to these estuarine areas and the only thing that is different (for sharks) after millions of years is the human factor," Mr Mitchell said.
"The estuaries are throwing up lots of nutrients, particularly after rain."
Windang Beach sits astride the opening to Lake Illawarra while Towradgi Beach is just north of the Fairy Creek inlet, which may have contributed to yesterday's sightings.
Mr Mitchell also warned beachgoers against taking an early-morning dip.
"It is best not to go out into the ocean at dawn or dusk because that is when these animals are out there looking for their food."
The sightings came two days after a 51-year-old West Australian man went missing off the coast of Port Kennedy, near Rockingham. Brian Guest was snorkelling 30m off the coast with his son, Daniel, when it is believed the shark struck. Witnesses reported seeing a shark thrashing in the water.
On Sunday, beachgoers swimming near North Stradbroke Island, off the coast of Brisbane, were sent from the water after a pack of 30 sharks, believed to be bull sharks, were spotted in waist-deep water.
Mr Mitchell said shark attacks and fatalities were on the rise "not just around the world but in our own country".
"The interaction over the last 30 years (between sharks and humans) has been extraordinary and I believe it has created a curiosity amongst the species which draws them closer to people in the water," he said.
"But don't be frightened, enjoy the water ... but be vigilant."