Wichien Jungrungruang said quality checks of sea water on 12 Samet Island beaches and bays found that the levels of oxygen and heavy metals were below the hazardous standard.
Polycyclic aromatic hydrocarbons (PAHs) were also below the standard level and would not affect marine lives in the area, he said.
Collection of samples on September 3 at 11 beaches on the island found the level of total petroleum hydrocarbon (TPH) at 0.05-0.29 microgrammes per litre – lower than the sea water quality standard, he said.
He warned tourists, however, against swimming at Prao Bay where the TPH level, measuring at 3.30 microgrammes per litre, was higher than the safety standard.
Mr Wichien said the quality of sea water near Prao Bay and other beaches has gradually improved and should be back to normal later this month.
The Natural Park Department will be asked to close Prao Bay until next month, he said.