France, Aug. 4 -- At a beach near Algiers, brown algae native to the Pacific Ocean cover the golden sand, posing a threat to ecosystems native to the area and their stench repelling swimmers at the peak of summer.

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 t...