Victorian lifesavers are bracing for a record shark season, with more sharks already spotted off beaches than in the last three or four seasons combined.

An "uncanny" perfect storm of water and weather conditions is bringing the sharks closer to the sand than usual, and in greater numbers.

With the holiday season still fresh, already more than 40 sharks have been seen near swimmers.

"Mate, it's probably more than three seasons, four seasons put together," says Paul Shannon, Life Saving Victoria's general manager.

On 37-degree Christmas Day, as Victorians flocked to the water, lifesavers spotted 12 sharks west of Anglesea and up to 20 near Fairhaven, forcing them to order swimmers out of the water. Sharks have also been seen at Ocean Grove, Moggs Creek, and Patterson River in Port Phillip Bay.

Sharks were spotted at Chelsea Beach on Wednesday and Fairhaven on Friday, forcing its closure. Point Lonsdale beach was closed after a shark was spotted 500 metres offshore on Friday afternoon.

Three environmental factors are driving the shark surge, experts say.

First, sharks tend to follow currents of warm water – often because that's where their prey swims.

This year's sea-surface temperatures around Australia were the highest on record since 1900, according to Bureau of Meteorology data. Victoria's entire east coast experienced record sea temperatures, with the rest of the state strongly above average.

Exacerbating this factor, rainfall was up 19 per cent this year, and 2016 was among the wettest years on record.

"We have had a lot more rainfall this winter, so there would be a lot more runoff, which makes for nutrient-rich waters," says Kent Stannard, founder of great-white research organisation White Tag.

"That makes for good conditions for all sorts of marine life, including sharks."

The nutrient-rich waters encourage micro-organism growth, making them good feeding ground for smaller fish – which in turn are the natural prey of sharks, LSV's Mr Shannon said.

"Uncanny" still-water conditions also contribute, says Mr Shannon.

"We have had a lot of very still water, which is really quite unfamiliar, uncanny for this time of year. Normally this time we get a lot of sea breezes, there is a lot of chop on the water, but this time of year there is been a lot of dead glassy days."

Most of the sharks spotted have been bronze whalers. They tend to be pack animals, unlike solitary great whites, and they also enjoy sunbathing in shallower waters – factors that may have increased the number seen this year.

"On the scale of dangerous sharks, the bronze whaler is not up there with the white pointers and tiger sharks. But it certainly sits in that next tier where there have been reports of attacks," Mr Shannon said.

Point Lonsdale Beach was closed due to shark sighting within 500 metres of flags. Photo: Anna Sublet

Life savers at Victorian beaches have been placed on high alert to watch for shark activity from their patrol towers, and the organisation is using two helicopters to sweep the coastline.

Ken-Leon Yap, a Fairhaven lifeguard, had to pull up flags at his beach Friday morning after a chopper spotted a shark offshore.

"I've been life-guarding for four years now, and this is definitely the most shark-sightings I've ever had to deal with," he said.

Mr Shannon said the safest place for shark-wary swimmers was always between the flags, where the level of shark vigilance was highest. He encouraged Victorians to download the VicEmergency app, which has real-time shark sighting and beach closure information.

There have been 12 shark attacks in Victoria since 2000, according to the Global Shark Attack database, with the most recent by a bronze whaler at Tyrendarra Beach near Portland in July 2015.