Helicopters patrolling the bay put out an alert after spotting the shark at Chelsea Longbeach, near Edithvale just after 1pm.

It's the second confirmed shark sighting in the bay this summer.

A 2.5m shark was seen at the mouth of the Patterson River at Carrum Beach on Boxing Day.

Many of Melbourne's beaches, unswimable after last week's storms swept faecal contaminants into the water, had been declared safe for swimmers on Wednesday.

Another shark was seen on Wednesday off Point Addis, near Anglesea on the Great Ocean Road, about 11:55am, according to Life Saving Victoria.

Helicopters patrolling the beach sounded a siren to alert swimmers to evacuate the waters.

Paul Shannon, General Manager of Life Saving Victoria, said it could not be ascertained from the helicopter what type of sharks these were, but based on expert analysis of footage from the past weeks, they are most likely bronze whalers.

Wednesday's sightings come after a Christmas Day in which up to 32 sharks were seen off Victoria's coastline. 

Mr. Shannon noted that sharks are sighted frequently, but helicopters only sound sirens when the sharks are positioned close enough to a shore where people are swimming, and could pose a potential risk.

Where possible, he added, the helicopter pilots try to herd the sharks out to sea.

Those enjoying the beaches this summer have been urged to stay informed about the risk of sharks, leave the water as soon as an alarm is sounded, and avoid returning to the water until the emergency notification is removed from the Vic Emergency website or smartphone app.

Additional tips for being shark-safe include swimming between the red and yellow flags, recognising danger signs – such as large schools of fish, seals or wildlife behaving erratically – and to never swim or paddle alone.