Invasive fish in river crisis - 18th May 2026

Authorities in Indonesia have embarked on a massive campaign to rid the country's waterways of the sapu-sapu, or suckermouth catfish. Native to South America, this tropical species had been introduced to Southeast Asia as a means of keeping fish tanks clean.

However, reaching up to 50 centimetres when fully mature, many outgrew their tanks and were released into local rivers by their owners. Since female sapu-sapu lay thousands of eggs every year, they've been able to outbreed the indigenous freshwater fish in the wild and have also outcompeted them for food.

Meanwhile, another secret to this invasive species' success has been its ability to survive in oxygen-poor and polluted waterways. More than half of Indonesia's rivers are heavily polluted and, according to the UN Environment Programme, two of the country's major river systems rank among the world's dirtiest.

One of the most severely affected areas has been Indonesia's water-stressed capital, home to 42 million people. Local residents, sanitation workers, fishing ministry workers and soldiers in Jakarta are pooling their resources in an effort to clear the surrounding waterways.

The result's been that, just in South Jakarta, 5.3 tonnes of sapu-sapu have been extracted in two weeks. Collected in wide nets stretching across the flowing waters, the sapu-sapu are separated from indigenous species, decapitated and then buried, with local fish returned to the river.

Whilst some activists contend that using them to produce fish leather and animal feed would be less wasteful, Muhummad Anwar, the mayor of South Jakarta, cites the dangers this poses.

Muhammad Anwar: "It contains heavy metals and is dangerous to humans."

Rather than being something confined to Indonesia, the impacts of invasive species are felt globally, with the UN producing an assessment in 2023 that they cost $400 billion a year in lost income and damages.