The agencies concerned on Sunday joined together to rid the beach of the oil slick which covered several kilometres of oceanfront in the renowned seaside resort of Pattaya.
The beach has returned to normal, with only a little oil slick left after the cleanup operation. However, shops along the beach said that few visitors have returned.
They said the oil slick severely affected tourism as well as speed boat service. Tourists no longer feel swimming is safe after many suffered from skin irritation and were taken to hospital for medical treatment.
The origin of the new oil slick, discovered Thursday night, remains unknown, but it was thought to have released from ships that illegally dumped their used oil into the sea at the Bang Pakong estuary or offshore at Si Racha district.
Marine Department director-general Sorasak Saensombat earlier said he had instructed officials to investigate the case.
For long term solutions to illegal oil releases, Mr Sorasak said the department will consider increasing the severity of the penalty from the current fine of Bt60,000 and 3-year imprisonment.
He said the offenders would also have to pay for any clean-up costs, expressing his belief that harsher punishment will help reduce the problem.