Sea foam, red algae - How long until South Coast flood damage disappears?

Beaches became bubble baths, or carpetted in red algae. Our sapphire blue waters became murky brown and putrid.

What caused each of these phenomena, and how long until our natural coastline is back at its shiny best?

Australian Community Media has the answers to all your post-flood questions.

How did my beach become a bubble bath?

The ocean appeared to have the head of a poorly-poured beer recently, yet Associate Professor at Macquarie University's School of Natural Sciences Jane Williamson said the sea foam was completely natural. She said the foam on our beaches was actually caused by small particles in the water itself, formed in a process similar to how bubble baths work.

These small particles can include algae, proteins, fats, bits of skeletons, and plankton, and also non-natural particles such as fertilizers, oils and detergents. Recent wind, rain and large swells were the perfect conditions to act as a big churning machine.

"The bubbles form because sticky molecules called surfactants cling together, along with these particles," she said. "The most natural formation for these sticky particles is a sphere. The spheres turn into bubbles, and the bubbles turn into sea foam."

"Once the conditions subside and the sea foam is left on the beach, it slowly "pops" and disappears - like a bubble bath."

A/Prof Williamson said the process of foam breaking down could take hours or days. Most foam along the south coast has already cleared.

Why are the beaches red?

The algae that coats the coastline is known as 'wrack' and will break down organically over several weeks if it isn't pulled back into the ocean by high tides.

A/Prof Williamson said the red algae was common sub-tidally in the Jervis Bay area and that last week's strong tidal surges had pulled out algae and thrown it up onto the beach.

While it is smelly and can contain maggots or other tiny crustaceans, this wrack plays an important role in the ecosystem according to A/Prof Williamson.

She said the algae was chemically rich and fundamental in the circle of life. She said it was normal on beaches, and that it was difficult to estimate how long the algae would remain on the beach.

Why does the water get so brown?

Every time there is heavy rain, waters along the south coast are stained brown for days, sometimes even weeks.

The south coast has very dispersive sediment easily mobilised by floodwaters, and this is why the local waterways turn brown so quickly in heavy rain events.

Eurobodalla Shire Council advise that "following wet weather, swimmers should avoid swimming up to three days after rain, and when the water looks murky and unclean".

READ MORE: Why is our water brown, and when will it be clear again?

How are the animals?

Animals were as shocked as humans by all the recent flooding. Local wildlife have had their habitat flooded and been exposed to the full ferocity of the elements. WIRES volunteer Rachael McInnes said animals were seeking any dry location they could find, which may include venturing into houses and sheds.

She said if you stumbled upon an animal trying to find shelter, do not be alarmed and contact your local wildlife group.

READ MORE: Heard of the 'drowned rat'? What about mud-caked kingfisher, water-logged wombat?

What about the animals in the water? Can fish keep breathing?

Eurobodalla Fishing and Boating Network chair Max Castle said the brown colour of the water was not all bad news for fishing in rivers along the coast.

"It is good for our lakes to get a good flush out," he said.

"Fishing picks up after a good wash out."

Mr Castle said intermittently closing and opening lagoons - such as Coila Lake in Tuross Head - had also been cleaned by recent rain.

"The prawn season is probably over for the year," he said. "But it could mean a good year next year."

That is because ocean water flowing into the river allows small prawns and prawn larvae to enter.

He said it was important to be careful fishing, especially with rough seas continuing along the coastline.

The colour of the sea foam is a good indicator of how it will effect aquatic life, according to A/Prof Williamson.

"Brown sea foam usually has lots of stuff in the foam that the sea could do without, like detergents and terrestrial sediment," she said. "This may have a negative impact on the marine life if consumed in quantities."

"If the sea foam is beautiful and white it is not likely to be caused by terrestrial runoff, and it's probably perfectly fine and could even offer a yummy source of food for fish."

Red sea foam is usually algal blooms, which can be dangerous to marine life.

Phew, so all marine animals are going to be okay?

For many, the south coast is synonymous with oysters, and yet all the flood water has prohibited farmers harvesting oysters.

"You are what you eat," is especially true for oysters, which act as filters eating nutrients from the water. The La Nina wet summer had already forced some oyster farmers to close along the coastline, and last week's torrential storms only compounded the situation, bringing dirty water into the river, and changing the salinity. Batemans Bay Oysters director Jim Yiannaros said he would not be able to harvest his oysters for another two weeks at best.

Expect restaurants and suppliers to be low on oysters in the coming weeks.

READ MORE: Torrential rain causes local oyster shortage