Tangerang – Tangerang city administration should carefully monitor businesses that channel wastewater into the Cisadane River during the rainy season, an environmentalist warns.

During periods when river levels are high, businesses could easily dump wastewater without being noticed, environmentalist Ahmad Sirojudin said Monday.

"It's obvious if someone deposits liquid waste during the dry season when river levels are low because the water changes color and dead fish may float to the surface," he said as quoted by Antara.

"Dumping it when the river is full or overflowing would go unnoticed." He said the only proof that untreated wastewater was illegally dumped would come if residents began to suffer skin diseases.

Last week, the Tangerang municipal environmental agency reported that a number of manufacturers had allegedly dumped untreated liquid waste into the Cisadane. The businesses are located in Karawaci, Jatiuwung, Periuk and Cibodas.