The beaches where things are going swimmingly

Ariana Tobotabo (3) Aerone Tabotabo (9) and Kat Manzo (7) enjoy Sorrento front beach. 3rd January 2018 The Age Fairfaxmedia News Picture by JOE ARMAO
Ariana Tobotabo (3) Aerone Tabotabo (9) and Kat Manzo (7) enjoy Sorrento front beach. 3rd January 2018 The Age Fairfaxmedia News Picture by JOE ARMAO
Shark  Warning and Whale remains Warning Sorrento back beach. 3rd January 2018 The Age Fairfaxmedia News Picture by JOE ARMAO

Shark Warning and Whale remains Warning Sorrento back beach. 3rd January 2018 The Age Fairfaxmedia News Picture by JOE ARMAO

Shark  Warning and Whale remains Warning at Jubilee point near Sorrento back beach. 3rd January 2018 The Age Fairfaxmedia News Picture by JOE ARMAO

Shark Warning and Whale remains Warning at Jubilee point near Sorrento back beach. 3rd January 2018 The Age Fairfaxmedia News Picture by JOE ARMAO

If you're planning a trip to the Mornington Peninsula over the next few days, you have several beaches to choose from in the Sorrento area.

You can go to the beach that's enclosed by Port Phillip Bay - Sorrento front beach, which has been one of the bay beaches with the best water quality so far this summer.

Or you could take a dip a couple of kilometres away at the Sorrento back beach that backs onto Bass Strait.

The lifesaving patrol captain there, Howard Draper, says this beach has a rough and rigorous surf, making it much different to the calm and shallow waters you can expect at the front beach.

But at the moment, you'd best avoid St Paul's beach or Diamond Bay, a pair of secluded and unpatrolled spots nearby, not far from where a dead whale washed ashore at Jubilee Point in November.

The animal's rotting carcass has since slid back into the sea, but Fisheries Victoria is advising swimmers to be careful in this area because the remains could attract feeding sharks.

The beaches have not been closed, but warning signs in the area urge people to stay out of the water for their own safety.

Ian Parks of the Victorian Fisheries Authority said remnants of the dead whale were still being detected in the area, so the beaches were still being monitored for shark activity.

But the water is fine at Sorrento front beach. It has been named one of this summer's best beaches based on the Environment Protection Authority's most up-to-date water quality data, with 21 days out of 31 in December delivering good conditions for swimming.

Only a quartet of beaches on the Bellarine Peninsula have garnered more favourable forecasts from the EPA. Eastern beach, Portarlington, Santa Casa and The Dell each recorded 22 days of pleasant conditions in December.

The EPA beach reports use a combination of weather forecasts, pollution reports and historical water data to predict water quality at 36 popular seaside locations.

While the best beaches are ranked based on predictions and not daily samples, the forecasts are accurate 98 per cent of the time and are a strong indicator of water quality.

Two beaches have recorded less than favourable forecasts so far this summer - Williamstown and St Kilda, where conditions have not been suitable for swimming more than half of the time.

These locations, along with Brighton beach, had also been experiencing algal blooms earlier this summer.

The EPA's chief environmental scientist, Andrea Hinwood, said the blooms had caused the water to turn a red-brown colour, and that swimming when algae concentrations are high can cause skin irritation.

The beaches have since returned to normal. The cause of the elevated algae levels was likely to have been nearby stormwater drains pumping nutrient-rich run-off into the bay, she said.

After heavy rains, the EPA will typically advise Melburnians to avoid swimming at all Port Phillip Bay beaches for about 48 hours, by which time any gastro-causing bacteria washed in by stormwater will have disintegrated.

But after more than 60 millimetres of rain fell in Melbourne at the start of December, there were six days in a row in which water quality was poor at every bay beach.

Dr Hinwood said the poor conditions lingered because of the sheer volume of contaminated water that flowed into bay, forming a 15-kilometre plume.

Melbourne is set to experience three consecutive hot and sunny days starting on Thursday, culminating in a 41-degree scorcher on Saturday, and the beach forecasts are promising.

The EPA expects good water quality for swimming at all 36 bay beaches on Port Phillip Bay on Thursday.

This story The beaches where things are going swimmingly first appeared on The Age.