Oil palm plantations and mining companies were the biggest polluters in the country last year, an environmental group said.
Mukri Friatna, head of advocacy for the Indonesian Forum for the Environment (Walhi), said on Monday that firms in these sectors polluted at least 57 out of 65 affected rivers in 2010.
"Oil palm plantations ranked first as producers of pollutants, followed by mining companies," he said.
The plantations, he added, were responsible for sullying at least 31 rivers across the country, while coal companies dumped toxic waste and other harmful residue in at least 19 rivers. Mukri said gold miners were responsible for polluting seven more rivers.
He said the affected rivers did not include those in Jakarta and other urban areas, which were already heavily polluted by domestic and industrial waste.
Walhi reported last year that at least 65 rivers, five lakes and five marine areas were contaminated by waste from private and state-run companies, an increase from 53 polluted rivers in 2009.
Polluted lakes include Situ Rawa Badung in West Java, which was contaminated with mercury; Sembuluh in Central Kalimantan, which became a dumping ground for crude palm oil waste; and Penantian in South Sumatra, which was tainted by slick from a nearby coal power plant.
These toxic pollutants decreased the amount of oxygen available to organisms, caused imbalances in natural processes and made the water unsafe to drink or use, Mukri said.
Besides being extremely hazardous to health, these substances also harm the environment, killing off fish, marine life and micro-organisms, by starving them of oxygen.
But Mukri said that only 14 pollution cases reported by Walhi had been brought to court.
The dumping of industrial waste into rivers – whether deliberate or out of negligence – is illegal under the 2009 Environmental Protection and Management Law. The law also penalizes regional administrations that fail to take any action against polluters.
Walhi has urged the state to revise a law on environmental impact analysis (Amdal) so there would be stricter requirements for companies seeking to set up factories or processing plants in Indonesia.
The group also called on the government to issue its long-awaited strategic study of the environment.