Batteries, nets and ropes that have been left in the ocean from fishing are lethal for decades to the sea life around them.
SIOBHAN ROBBINS: These divers are on a mission. Part clean up, part rescue. The area they're working in is in the Gulf of Thailand, and this is their target. The thousands of tons of old fishing nets, dubbed ghost nets, littering the ocean every year.
INGPAT PAKCHAIRATCHAKUL: Because those are actually really dangerous because once they are fallen into the ocean they can stay afloat for decades. So either marine animal will be entrapped there or they will digest those nets and then that would lead to health problems that eventually lead them to die.
SIOBHAN ROBBINS: Discarded fishing gear is one of the deadliest forms of ocean plastic pollution, harming 66% of marine mammal species. Once the ghost nets are spotted, the divers have to measure and log them. Trapped animals, alive or dead, are also recorded. The nets are then carefully cut free and collected. While some are tangled deep below the surface, others are much easier to find. This is a huge problem. We swam about 10 minutes and we've already found our first net. Around 50,000 small fishermen carry these alone in Thailand. The amount that are littering the ocean floor is still unknown. The collected nets are return to the boat, bag after bag they keep mounting up.
RAHUL MEHROTRA: What we can see there's a variety of pieces of net and rope, and obviously a single fairly sizable battery.
SIOBHAN ROBBINS: Back on the land, the nets are separated and cleaned, unwitting catches inspected.
RAHUL MEHROTRA: So what we can see here is clearly a dead individual. There's no animal left inside, so it has been entangled in the net and been unable to escape. I've just spotted another one also dead.
SIOBHAN ROBBINS: Once clean, the nets are given a new life. Shredded and reprocessed, some have been turned into COVID visors. 47 fishing communities in Thailand are helping with the cleanup, getting paid for the nets they salvage. But the challenge is huge.
RAHUL MEHROTRA: We have the Band-Aid solution at the beginning, which is to actively remove the nets. That deals with the symptom. It prevents further things from getting entangled. Finding the source of the problem is another matter entirely.
SIOBHAN ROBBINS: Discovering the source, first requires understanding the scale of the problem. So campaigners and scientists will meticulously log every ghost net they spot in the hope they can find a way to finally rid the sea of this deadly rubbish. Siobhan Robbins, Sky News, Thailand.