From the Jakarta Globe, 4 May 2016,
Jakarta. Fish farmers at Lake Toba in North Sumatra were shocked to find their nets filled with dead fish on Tuesday night (03/05).
The fish farms located at Haranggaol in Simalungun district commonly raise carp and Nile tilapia. Many people living around Lake Toba have taken up fish farming in recent years.
According to local fish farmer Parlaungan, the incident resulted in a total estimated loss of 320 tons of fish, worth billions of rupiah.
"This has never happened before. Usually we can count the number of dead fish we remove per day. But this time, all the fishes in the nets were dead," Parlaungan said on Tuesday.
Another farmer, Hasudungan, believes the fish died from a lack of oxygen in the water.
"The oxygen content in the cage is only 0.8 [parts per thousand], while the standard is 2. We can go bankrupt because of this," Hasudungan said.
On Wednesday, Simalungun's department of fishery and livestock sent a team of experts to Haranggaol to investigate the high number of fish deaths.
Officer Jarinsen Saragih said his team was still unable to determine the reason, but that they suspect that the incident was indeed caused by a lack of dissolved oxygen in the water.