Tourists were disgusted to see a beach covered in a gruesome dark green plankton bloom in Thailand.

Aerial footage shows holidaymakers standing by the shore, looking bewildered as the thick, murky water laps at the sand at Bang Saen Beach in Chonburi on April 10.

Some of the swimmers took a dip in the discoloured water, but others chose to stay away.

By 5pm that day, more visitors left the area as they were afraid to touch the ocean in case it could be bad for their health.

Tourist Suphakorn Siritasanakul, 49, said: 'I brought my family from Pathum Thani to visit the beach but when they saw the green colour they didn't want to go near it.

'We wanted to swim but it looked disgusting.'

Department of Marine and Coastal Resources officer Kritkhajorn Aunjai, 34, arrived to collect samples later.

He said: 'The water turned green due to a plankton bloom likely caused by an increase in nutrients.'

The officer added the bloom might have been pushed from the coast by rain and wind a day before.

He said: 'The green colour could disappear in less than a week.'

While the results could not yet pinpoint the specific type of plankton, he added it could cause skin irritation although tourists should not panic.

He said: 'The water would return to normal on its own.'

The Institute of Marine Science at Burapha University said that the phenomenon is scientifically known as Noctiluca scintillans. 

The green water was not caused by toxic substances but rather by extremely small plankton and not visible to the naked eye. 

Despite their size, these plankton can multiply rapidly, doubling in number and turning the sea green. 

Depending on nutrient levels and sunlight, the effect may last anywhere from three to seven days.