Thailand's popular tourist island of Ko Lan turned green as discolouration kept some swimmers out of the sea altogether. (Facebook pic)

KO LAN: The sea off Thailand's popular tourist island of Ko Lan turned a bright, pungent green this week as heavy rains and floods helped spark a plankton bloom that kept some swimmers on shore.

Dense patches of green could be seen stretching along parts of the coast, with jet skis floating in discoloured waters around the island in the northern part of the Gulf of Thailand, while other stretches of the shoreline were unaffected.

"What we're actually seeing with the naked eye is a colour that comes from a type of plankton called Noctiluca," said Arvut Munhapon, a senior researcher and head of marine environmental research at the Marine Science Research Division, Institute of Marine Science, Burapha University.