Sea off Thai island turns vivid green in plankton bloom

The waters surrounding Ko Lan, an island off the coast of Thailand, have turned a vivid shade of green, after a bloom of plankton coloured the sea in the area.

Plankton blooms, sometimes referred to as algal blooms, occur when microscopic marine organisms multiply rapidly in a body of water, often in response to favourable conditions such as nutrient availability, water temperature and sunlight. Depending on the species of plankton involved, blooms can turn water various colours, including green, red or brown, and are a relatively common, if visually striking, natural phenomenon in coastal waters around the world.

Why blooms happen

While many plankton blooms are harmless and even play an important role in marine food chains, feeding fish and other marine life, some can have negative effects, including depleting oxygen in the water or, in certain cases, producing toxins harmful to marine life or humans. Local authorities and environmental monitors typically assess blooms to determine whether there is any risk to swimmers, fishing or local ecosystems.

Images of the green waters off Ko Lan quickly drew attention for their unusual, almost luminous appearance, with the island known as a popular tourist destination near Pattaya. It was not immediately clear how long the bloom was expected to last, or whether authorities had issued any specific guidance in response to the discoloured water.

Blooms of this kind generally subside on their own once the conditions that triggered the rapid growth of plankton change, such as a drop in nutrient levels or a shift in water temperature.