JAKARTA – Jubilant cheers erupted across Indonesia’s bustling capital on Friday as residents, city officials, and environmental volunteers united in a collective effort to pull hefty nets of invasive fish from a local reservoir. This operation marks a significant step in the ongoing battle against the so-called “janitor fish.”

Authorities are determined to extract a minimum of 10 tons of these fish from Jakarta’s waterways. This ambitious initiative aims to restore the ecological balance in the Ciliwung River and draw public focus back to the critical issue of water quality.

The cityscape, with its polluted river stretching from concrete embankments to canals flanked by skyscrapers, is home to these fish, whose dark forms cling to the river walls. With their armored bodies glinting a dull brown beneath the murky waters, they give off an almost prehistoric aura.

Known scientifically as Pterygoplichthys and locally dubbed “sapu-sapu,” these suckermouth catfish are not native to Indonesia. Introduced decades ago for aquariums due to their algae-eating capabilities, they were eventually released into the wild and have since thrived in Jakarta’s polluted rivers. These resilient fish can reach lengths of up to 50 centimeters (nearly 20 inches) and have a lifespan of 10 to 15 years.

Experts have long cautioned that unchecked growth of invasive species like the janitor fish can significantly disrupt freshwater ecosystems, especially in densely populated urban environments such as Jakarta.

Dian Rosleine, an ecologist at the Bandung Institute of Technology, highlighted the fish’s remarkable adaptability. “Even in polluted conditions, the janitor fish can survive where other species cannot,” she noted, underscoring the resilience that allows these fish to dominate local waterways.

“So, these fish are biological indicators that the water is in poor condition,” she said.

The Ciliwung once carried clear water from the mountains of West Java into Jakarta. Today, it flows through dense neighborhoods, carrying untreated household waste and industrial runoff. Concrete walls replaced riverbanks. During dry months, the water warms and slows — conditions that favor janitor fish over native species, Rosleine said.

Jakarta authorities have responded with mass removals, targeting the janitor fish in city waterways. The campaign began last week.

The cleanup drive, ordered by Jakarta Gov. Pramono Anung, was carried out simultaneously in all five administrative cities of the capital, involving hundreds of personnel, including firefighters, disaster officers and local residents. They have netted and buried more than seven tons of janitor fish across the city within a week.

The cleanup on Friday at a 6-meter-deep (19-foot-deep) reservoir in East Jakarta’s Ciracas neighborhood drew curious crowds as city workers collected about 320 kilograms (705 pounds) of the fish.

Piles of wriggling janitor fish filled red barrels along the reservoir — tangible proof that something, at last, was being done.

“The janitor fish populations have reproduced at a notable level while also feeding on native species,” East Jakarta’s mayor, Munjirin, told reporters when visiting Friday’s cleanup. “The impact extends beyond ecosystem destruction, contributing to structural damage to riverbank and embankment walls.”

Munjirin, who like many Indonesians uses a single name, said that the coordinated operation marks the beginning of a sustained effort to control the species, with regular monitoring and removal planned to prevent further ecological damage.

However, he vowed a review of the program’s method after the Indonesian Ulema Council, or MUI, raised concerns over perceived cruelty, pledging that all fish will be dead before burial.

While endorsing the cleanup, MUI’s fatwa commission warned that burying the janitor fish alive amounts to a violation of animal rights enshrined in Islamic teaching.

Authorities are still cautious about what happens next. As janitor fish are edible in some countries, concerns over heavy metal contamination mean they won’t be immediately approved for consumption in Jakarta. Instead, officials are exploring alternatives, including processing the fish into animal feed or fertilizer.

Anung said that the cleanup method will require the fish to be dead before burial at designated sites, with hygiene standards applied to block their return to rivers or trade.

The Jakarta governor noted that buried janitor fish can serve as natural compost and suggested adopting Brazil’s model, where the fish are turned into charcoal to generate greater economic benefits.

Yet experts caution that removal is only a beginning. Without improving wastewater management and reducing pollution, the river could quickly return to the same condition.

“The Ciliwung River requires rehabilitation, our major challenge that must be addressed,” Rosleine said. “Addressing the symptoms without tackling the root causes will not provide a lasting solution.”