The bags, with capacity ranging from 20-50 kilograms, were scattered over a 5-kilometre stretch of this popular beach, especially on Lan Hin Khao and the beachfront of Royal Hotel Rayong.
Beachside hotel and restaurant operators and local fishermen collected the bags for the authorities to dispose of later.
Fisherman Thavorn Imphrom said the sacks had showed up since Friday evening and suspected the bags were carelessly dumped in the sea by some contractor or fishing boat.
Khao Laem Ya-Koh Samet National Park chief Sumet Saithong said he had filed a police complaint, reported the incident to Rayong Governor Thani Samartkij and the National Parks, Wildlife and Plant Conservation Department and submitted some of the bags for testing to the authority, to see if they had toxic content.