Following a recent government call to help clear beaches swarmed by the seaweed species known scientifically as Rugulopteryx okamurae, several volunteers and charities have stepped in.
"When it washes up, we can't swim," said Salim Hemmedi, a 43-year-old vacationer at a beach in Sidi Fredj, where volunteers raked up heaps of the plant.
"We hope the situation will improve so that we can enjoy ourselves... and that children can swim in peace."
The alga originates from temperate waters around Japan and the Korean peninsula in the northwest Pacific Ocean.
It was first spotted in Algeria in late 2023, according to Lamia Bahbah, a lecturer and researcher at the National School of Marine Sciences and Coastal Planning.
And lately, some have noted that it has been increasingly washed ashore.
Youcef Segni, a marine engineer and biologist, said the algae proliferated at a significantly higher rate than in 2023 and 2024.
"They invade the habitats of other algae in the seabed, which leads to the disappearance of some species," he said, adding that it can also displace some native fish.
- Fast reproduction -
In France, Spain and Portugal, the Rugulopteryx okamurae species has also been observed.
Earlier this year, Spanish football club Real Betis introduced kits repurposed from the seaweed to raise awareness about the issue.
A 2023 study by the Marine Drugs journal said the alga's invasive character led to "a replacement of the native biota and an occupancy rate that reached almost 100 percent in some locations" in Portugal.
In Algeria, the plant has been spotted in at least three of the country's 14 coastal provinces, including the capital where 16 beaches are affected, authorities said.
"Are the waters suitable for swimming? Yes," said Environment Minister Nadjiba Djilali during the cleanup campaign, adding there were no records of the plant causing allergies.
Researcher Bahbah said stopping its proliferation was "unfortunately impossible at this stage".
She said the plant reproduces at a high rate, both sexually and asexually.
The species can reproduce through fragmentation, meaning new individual algae can develop from fragmented pieces of other Rugulopteryx okamurae algae.
The algae spread mainly by clinging to the hulls of boats, and the Mediterranean's moderate temperature favours the seaweed's fast reproduction.
"We are going to fight it," said Fella Zaboudj, a state engineer in marine sciences, adding that researchers were monitoring its spread, development and evolution.
Zaboudj said research was also under way to determine whether the algae could be repurposed as fertiliser.
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