Experts are baffled by the cause of an exceptionally large volume of "cornflake seaweed" that has washed up on southern Gold Coast beaches in recent days.

Key points: Experts say the seaweed will start to smell when it decays

Experts say the seaweed will start to smell when it decays The seaweed could remain on the beach and in the ocean for up to one month

The seaweed could remain on the beach and in the ocean for up to one month The Gold Coast City Council has sent inspectors to the affected beaches

The seaweed is piled up to 1 metre deep in some locations, trapping runners and swimmers who have become stuck in the algae.

Seaweed farmer and marine plant authority, Doctor Pia Winberg, from University of Wollongong said the seaweed influx was an annual event but this year the sheer volume was much greater than previous years.

"It is very unusual that it would come up in such masses on the beach," she said.

"The weed will start to smell as it decays but the weed will eventually break down and feed the marine food chain including fish.

"Some of that organic matter can be composted to promote plant growth.

Holidaymakers Greg, Sandi and Susan Wright said they will go to other beaches to swim to avoid the seaweed. ( ABC News: Jennifer Huxley )

"It could help to overcome drought stress, help gardens and encourage plants to become more resilient to drought."

Gold Coast Lifeguard superintendent Chris Maynard said the beaches remain open.

"The good news is there is nothing really to worry about as far as any nasties or dangers," he said.

'No-one would believe it'

Local runners and swimmers have struggled to make their way through the sludge after it washed up on to large stretches at Palm Beach this morning.

Ken Hall has lived in the area for 13 years and said the seaweed was not unusual but he had never seen it so dense before.

"We have had a few episodes of little bits of cornflakes in the water but this year it is in absolute plague proportions and down about Fourth Avenue it is knee-deep," Mr Hall said.

"I just took a photo of a guy to show him how deep it was because no-one would believe it."

Local runner Odette became trapped in the seaweed at Palm Beach and had to be pulled out by a passer-by.

"[I was] just running down the beach and you don't realise how dense it is becoming," she said.

She tried to break free of the seaweed but was stuck up to the top of her thighs.

Odette was running through the seaweed when she became trapped and was pulled out by Manny Menzies. ( ABC News: Julie Clift )

"I was over-thinking it ... thinking if I do fall down, no-one's going to see me," Odette laughed.

Manny Menzies came to her rescue.

"She needed a bit of help so I gave out a helping hand," he said.

"I was pretty confident I could get through it."

Climate change could be a cause

Dr Winberg said the influx could be the result of a range of factors, including climate change, but the cause is difficult to prove.

"Some seaweeds don't like the higher temperatures just like some land plants and they are suffering and get infections and start bleaching and these species do start migrating further south. We are seeing changes in seaweed populations due to that," she said.

Gordon Willits has lived at Palm Beach for more than 40 years and said he has never seen such a large volume of seaweed. ( ABC News: Jennifer Huxley )

"We also know that if there is an increase in nutrients plus a certain increase in temperatures some seaweeds may bloom even more than they have in the past.

"There can be big shifts due to climate change and this may be something related to it, but it is a little bit like the weather and the climate differences.

"It is very hard to pinpoint it exactly to climate change when we see it this once.

"If it continues to happen and it continues to increase then research and data will slowly start to show us that this is one of the — regime changes we call them — when the system starts to change in a consistent way," she said.

Seaweed may remain for up to one month

Dr Winberg said the volume of the biomass meant the seaweed could remain in the water and on beaches for up to a month.

"This period should not last more than a month in terms of it actually being created but because there is so much biomass, so much organic matter in this instance, it could be there are piles of seaweed stuck on certain beaches and bays for a while if they get entrapped there," she said.

"In those cases it just means the decaying mass may be around longer than usual.

"But if the currents and flows end up bringing it back out to sea or if there are some storms with big waves it could disappear very quickly."

Gold Coast City Council has sent inspectors to the beaches that have been impacted.