Health alarm as tide of rotting seaweed chokes UK holiday beaches

Potentially lethal to fish and dangerous for humans, the summer’s toxic invader is caused by warming seas and strong winds

When Owen Francomb from Margate set out on a walk with his dog Gertie along Kent’s picturesque Thanet coast early this month, he didn’t imagine he’d need to be rescued from a tide of toxic sludge. But on the beach at Newgate Gap, French bulldog Gertie started sinking into a thick carpet of rotting seaweed and began to panic.

“She couldn’t move,” Francomb. says. “So I scrambled down the slipway and jumped down on to the beach, expecting the seaweed to be a foot deep, but it came up to my belt. I really struggled to wade through it.” Another dog walker had to help him and Gertie out of the stinking slime.

Over 1,000 tonnes of seaweed have been removed from beaches between Minnis Bay and Broadstairs by Thanet district council – at a cost of £65,000 – in just five weeks from the beginning of July this year, compared with a reported average of between 400-800 tonnes in an entire season.

“We do typically get seaweed blooms as the weather warms up, so residents are used to it,” says Amy Cook, founder of the community initiative Rise Up Clean Up Margate which organises regular beach cleans and local environmental campaigns. “This year, however, the smell of seaweed has hung over the whole town, which does not usually happen.”

Margate is not the only place to suffer. Weymouth in Dorset is another tourist town which has suffered from an unusually large amount of rotting seaweed on its beach this summer.

The seaweed has benefited from ideal growing conditions this year including extreme marine heatwaves in the North Sea. There have also been unusually high tides and strong winds, beaching excess seaweed in the south-east of England. Warming oceans mean that warm-water species are spreading, particularly more fleshy species such as kelp and seagrass.

Seaweed is a macroalgae that grows only in seawater. As it decomposes it can release the gas hydrogen sulphide which affects fish – and can be lethal. It also cause eye irritation and respiratory problems in humans.

Florida-based researcher Dr Brian Lapointe has, since 1973, been studying seaweed blooms like those found on the Kent coast and their relationship to wastewater He says the smell caused by hydrogen sulphide is a “real issue” and “people need to take precautions if they’re living in an area with those odours”.

“[The gas] can affect the electronics in your house because it forms sulphuric acid,” he says. “In the Caribbean, where Sargassum seaweed has been such a problem, people have lost electronic appliances: air conditioners, all kinds of things.”

UK government guidelines state that an average person experiencing prolonged exposure can experience “notable discomfort”. Higher quantities could induce headaches, bronchial constriction, fatigue and dizziness.

Thanet district council cannot remove the rotting seaweed from some locations due to the presence of a chalk reef which is a marine conservation zone. Current advice for residents is to keep windows closed and “avoid exercising outdoors when the smell is present, particularly if your breathing rate increases”.

Environmental science expert Professor Daniel Franklin monitors the effects of unnaturally elevated nitrogen levels in Poole Harbour. “The main concern with big accumulations of seaweed is that there are potentially large, and negative, ecological changes, as well as negative consequences for some human activities like tourism,” he says.

The Kent area also suffers from nutrient enrichment of coastal waters due to sewage discharge as well as agricultural run-off.

In 2023, between Herne Bay and Whistable alone, Southern Water has already released sewage into the ocean at least 374 times via storm overflows – 181 of those occurring since the beginning of May in the busy summer season – according to figures published by Surfers Against Sewage.

In Broadstairs, where the numbers of E coli and intestinal enterococci colonies this summer have been as high as 960 per 100ml, lifeguards are sometimes forced to keep people out of the water rather than make sure they’re safe within it.

Seaweed blooms have been linked to health issues internationally. Across the Channel in Brittany, the proliferation of green algae along the coastline, thought to be caused by extensive factory farming, was the subject of a bestselling graphic novel, Green Algae, by journalist Inès Léraud in 2019. A film adaptation of the book was released this summer.

SOS Whitstable founder member Bryony Carter says the protest group has noticed “a substantial increase in seaweed over the last three years”, adding: “It may cause issues for swimmers in the future if it continues to grow at the rate we’ve seen.”

In a statement, Southern Water said it was “committed to reducing use of storm overflows and working to increase our wastewater treatment storage capacity along with nature-based and engineering solutions to divert rainwater away from the sewer system and back into the environment”.

Neither they nor Thanet council could provide readings of hydrogen sulphide gas in Kent.