IT'S guilty of looking crook and causing an almighty stench, but innocent of leaving swimmers with itchy skin.

The stunning white sand beaches of Jervis Bay have been swamped with a bloom of red algae washed ashore by sea breezes.

©The Daily Telegraph
Crimson coast ... the usually white sands of the beach at Huskisson at Jervis Bay is turned red by an algae bloom.

The algae has now died, begun to rot and is emitting a pungent odour in the process.

"It smells sort of like your compost heap but it can smell like dog poo," manager of nearby Booderee National Park, Martin Fortescue, said.

The algae, which is large, coarse and looks a bit like seaweed - it is nicknamed "cornflake weed" - is harmless to human beings.

However, concerned tourists have mistakenly blamed itchiness after a swim in the bloom.

Instead, the pernicious bites of sea lice breeding in the warm, autumn ocean - which, at its peak in temperature for this time of year, stands at about 24C.

Dr Fortescue said the national park's visitor centre had received a number of calls from people worried the algae had got under their skin.

"There might be a bit of a mix-up that people are swimming and getting bitten and thinking it's the algae," Dr Fortescue said.

"A few people were complaining about these bites and thinking that they were getting a reaction to the algae. It's not a health hazard. It just stinks."

The red algae leaves its mark on South Coast beaches for weeks at a time every couple of months.

It is also common in summer on the Mid-North Coast, particularly Port Macquarie, Crescent Head and South West Rocks.

But the last time a red spread of this size was seen in Jervis Bay was in the early 1990s.

Normally scattered around the bay, it is washed ashore by currents or on-shore breezes.

"It's just one of those natural occurrences," Dr Fortescue said. "If there was environmental or probable health issues we'd certainly let people know."

Locals first noticed the algae, which covers the sand at Huskisson, Vincentia and around to Callala Bay, over the Easter long-weekend.

An expected wind change is likely to wash the bloom back out to sea tomorrow and Sunday.

In the mean time, locals want to reassure tourists they are not in danger. In fact, the algae is a vital part of the ocean ecosystem.

"It's an important source of food," Dr Fortescue said.

The exact species of algae is not known, but it is not like fresh water algae, which can be toxic.