Another mass fish kill hits Indonesia’s largest lake


  • Indonesia’s Lake Toba experienced another mass fish death this week.
  • The incident cost local farmers hundreds of thousands of dollars, according to local government estimates.
  • The same thing happened in 2016, and not just in Lake Toba. Seventeen of Indonesia’s lakes are in “critical” condition, according to the government.
Millions of fish in floating cages died suddenly this week in Lake Toba, the biggest lake in Indonesia.
E. Naibaho, a local aquafarmer, noticed the fish in his floating pens moving in an odd manner in the days leading up to the incident. The water had become cloudy as well.
When he and his workers went to feed the fish on the morning of Aug. 24, none of them could be seen rising to the surface. They tried adding oxygen to the water, but it didn’t work. Before the long the fish began floating to the surface, dead.
“My capital is gone,” Naibaho said. “Hundreds of millions of rupiah.”
Another farmer, M. Nadeak, estimated the total losses for all the farmers at 5 billion rupiahs ($342,000). “Our economy is disturbed,” he said. “That’s going to create social problems.”
It was the second mass fish kill in as many years in the lake, which is located in North Sumatra. In 2016, millions of fish also turned up dead. Researchers attributed that incident to a sudden depletion of oxygen in the water, the result of a buildup of pollutants in the lake, unfavorable weather conditions and unsustainable practices by local aquafarmers.
Where the 2016 incident was concentrated in Haranggaol Bay of Lake Toba, this one happened in Pintusona, just off the giant island of Samosir in the center of the lake.
Other Indonesian lakes have experienced mass fish kills, too. In 2016, 3,000 tons of fish died suddenly in Lake Maninjau, West Sumatra — twice as many as that year’s incident in Lake Toba.
Both Toba and Maninjau are among the 17 lakes classified by the Indonesian government as being in “critical” condition, meaning they suffer from a host of environmental problems. Last year, government officials and academics from around the country gathered in Jakarta, the capital, to declare that a national body should be created to direct attention and funds to the nation’s more than 800 lakes.
With regard to the latest incident, an initial study by the district government indicated that the proximate cause of the fish kill was a rapid change in the temperature of the oxygen-poor water at the bottom of the lake, causing a sudden upwelling of water that made the lower layer rise to the surface, said Jhunellis Sinaga, the Samosir district government official in charge of fisheries. Waste produced by the fish farms contributed to the conditions behind the fish kill, he said.
Jhunelis estimated that the farmers had lost a total of 4 billion rupiah ($273,000), with 180 tons of fish dead. “Water samples, fish carcasses and more are being examined in the laboratory,” he said.
Local residents helped government workers carry the fish carcasses, with heavy equipment used to bury the fish.
The lake’s waters have been polluted by waste from the fish farms, according to the Lake Toba Lovers Foundation, a local NGO. The fish farms are run by local entrepreneurs as well as by several companies, said Maruap Siahaan, the chairperson of the foundation.
The foundation is demanding that the government halt all fish farming activities to improve the water quality of the lake.
As part of its plan to turn Lake Toba into a tourism hotspot, Indonesian President Joko Widodo’s administration has announced its intention to clean up the polluted lake, including by cutting down on the number of fish farms there.

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