Much of the trash I've seen in the waters around Phuket for over 25 years comes from the fishing boats - plastic, used neon light bulbs, oil, old line, fishing nets, etc. The local bottom trawlers have decimated the local fish stocks and other aquatic life. No-fishing zones are ignored. Same with the locals who fish from shore; they use the beach sea as their garbage can and leave their litter behind. I am no sympathy for these people.