City blames polluted rivers for fish kills in Jakarta Bay
Bambang Nurbianto, The Jakarta Post/Jakarta
The death of thousands of fish and clams in waters off Ancol Beach on Tuesday was likely caused by pollution in the city's toxic rivers, the Environmental Management Agency said.
Agency head Kosasih Wirahadikusumah said on Thursday the fish had likely died of asphyxiation.
"The phenomenon was probably caused by a drop in oxygen in the seawater. We do not find that it was caused by toxic materials dumped in the area," he said.
Tests had shown there was a significant drop of oxygen in the water to less than 1 milligram/litter of water, compared to the normal figure of 6 mg/l, he said.
A Bogor Institute of Agriculture (IPB) expert who was part of the investigating team, Tri Pantono, said the highly polluted Jakarta rivers flowing into the bay were the likely cause.
"The oxygen content in the blackish rivers is near zero. If such polluted waters comes in large amounts to the sea, it would surely affect the oxygen content in the seawater ... It is important to note the incident took place after heavy rains when the water flow of the rivers is usually high," he said.
The environmental management agency, together with experts from the IPB, the Agency for the Assessment and Application of Technology, and the Indonesian Institute of Sciences earlier took water and fish samples in the area for a laboratory examination.
Kosasih said the team estimated it saw about two tons of dying and dead fish floating in a one-kilometer radius between Marina Bay and Horison Hotel.
"We estimate more fish died there. The figures could be in the dozens of tons," he said, adding that the phenomenon reoccurred on Wednesday in a wider area.
Kosasih said many of the dead fish were popular with consumers, including milkfish, shrimps, and rays.
However, he said his agency had no information about the dangers of consuming the fish.
Thousands of fish, shrimps and clams died earlier in May in waters off Ancol Beach near the Kamal Muara area.
That time officials said the deaths were a natural occurrence; a boom in the population of phytoplankton sparked a corresponding increase in algae, causing a red tide phenomenon that absorbed the oxygen in the seawater.
Non-governmental organization Indonesian Forum for the Environment has voiced suspicion that the fish and clams were being killed by high levels of pollution in Jakarta Bay. The organization has alleged that industrial plants located in the area dump unprocessed waste into the bay.
A number of city councillors also raised concern that the fish were dying because of industrial waste being dumped into the bay by nearby plants, questioning why the red tide was not occurring in other coastal areas in the country.