Mountains of seaweed choke Sydney beaches as heatwave approaches

Mountains of seaweed have blanketed the sand on several Sydney beaches, where it will remain to rot to benefit the environment during a severe heatwave expected to hit the city this week.

Among the most affected beaches is Dee Why, where this masthead estimated piles of kelp to be up to 1.5 metres high at the deepest point – neck height for an average man or eye level for a woman.

Dr Aaron Eger at the University of NSW said excess seaweed on beaches typically occurred when there was a lot of seaweed in the water – for example, in summer when biomass was high. It also required swell or storms to rip it up and the right currents to bring it ashore.

“Over the last week, we have had ... lots of kelp, lots of swell, and some easterly swell to bring it onshore,” Eger said.

The other reason seaweed washed ashore was in the event of a big die-off, but Eger did not believe this had occurred this week.

In past decades, council contractors would have removed the excess seaweed from beaches, but these days the preferred approach is to leave it in place for its benefits to coastal ecosystems.

Northern Beaches Council referred this masthead to its website, where it states that seaweed is not removed from any beach because it is part of an important coastal process, supporting sand recovery on beaches and natural habitat.

“During large surf events, the kelp beds off the coast are dislodged and inevitably wash up along our many beaches,” the website says. “Due to the large wave action, the volume of sand on the shoreline is sometimes depleted and washed back into the ocean.

“The kelp washing up on the beach provides an ideal structural support for the recovery of the lost sand and in turn helps to rebuild the sand base. Whilst the rotting seaweed has a rather unpleasant smell for humans, it provides an important nutritional source for the habitat.”

Seaweed washed ashore by storms provided shelter and food for animals living on beaches, the NSW Department of Primary Industries and Regional Development said. The department regulates the removal of seaweed from beaches under the Fisheries Management Act.

Randwick City Council’s website says it removes 200 tonnes of rubbish and “excess seaweed” each year. The council does not have a policy of leaving seaweed to rot for its environmental benefit.

Randwick Mayor Dylan Parker said seaweed was sometimes left for a short time for the next swell or high tide to clear it, while other times it was removed and composted, depending on the quantity and condition.

“We pride ourselves on having a clean coast which is why we rake our beaches every single day for our residents and visitors to enjoy,” Parker said.

“Large amounts of seaweed can wash up, particularly after storms, and this is dealt with on a case-by-case basis as part of our daily beach inspection and cleaning.”

Sutherland Shire Council indicated that while small amounts might be collected by the beach cleaning rake during routine operations, large accumulations were usually left in place to allow natural processes to occur.

Temperatures are expected to soar above 40 degrees in western Sydney and well into the 30s on the coast from Wednesday this week, the Bureau of Meteorology said.

With James Brickwood

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