Black oil-like slicks were found floating in the sea and washing ashore at Jomtien Beach in Chon Buri on Monday, prompting authorities to warn tourists against swimming in the affected area.
The substance was reported along the shoreline and in seawater, with large amounts seen near Jomtien Beach and Koh Lan. Pattaya City officials deployed workers to collect samples, assess the extent of the pollution and begin cleaning up the slick.
Pattaya Deputy Mayor Manoch Nongyai said authorities were investigating two possible causes: an illegal discharge from a vessel or a substance drifting into the area from around Laem Chabang or Koh Lan. Officials from the Marine Department and environmental agencies have joined the investigation.
Pattaya City urged residents and tourists to exercise caution and avoid swimming at Jomtien Beach until the situation is assessed.