On Son Island in Vietnam’s Mekong Delta, Le Trung Tin scatters fish feed into his ponds, where dozens of snakehead fish leap through the surface in synchronised bursts. “I taught them how to do that,” he says proudly, tossing another handful of feed at his fish.

The scene looks idyllic, but Le’s fish farm is a reluctant response to an escalating crisis. For decades, he made his living fishing the Hau River, a distributary of the Mekong. But in recent years, plastic waste clogged his nets and strangled the fish. “I had no choice but to stop,” he says. “Everything was tangled – trash, nets, even the fish themselves. It was hopeless.”