Residents, city workers, and environmental volunteers in Indonesid’s capital on Friday hauled bulging nets of invasive fish to the surface of a reservoir to crack down on “janitor fish”. Authorities are seeking to remove at least 10 tonnes of the fish from Jakarta’s waterways, to restore balance to the Ciliwung River.

Janitor fish, or suckermouth catfish, known scientifically as Pterygoplichthys and locally as “sapu-sapu,” aren’t native to Indonesia. Imported decades ago for aquariums for their algae-consuming ability, they were later released and found a home in Jakarta’s heavily polluted rivers where they thrive.