Guddu Baba, who leads a movement to clean the river, Thursday said that brightly decorated idols accompanied with metal ornaments and plastic weapons were being ritualistically immersed in the river every year with no thought of the environment.

"We failed to understand the silence of the state government and other concerned authorities to initiate any move that idols are not immersed in the river. An alternate arrangement should be made for it," Guddu Baba said.

"It is a sad. Idol immersion is not only adding pollution to polluted river, but also posing a grave threat to water bodies, aquatic life and human health," he said.

Kartik Chakrabarty, another environmentalist said it was most worrying if idols immersing are harming holy river.

"Unlike past, now idols are made of plastic and fiberglass and are not nature friendly as compared to the clay, hay and cotton made ones of yore with natural colours," he said.

"They are all toxic and ruins the environment."

R.K. Sinha, a reputed expert on dolphins, said immersing idols, which contain large amounts of non-biodegradable material, is bound to affect the aquatic life of the river.

"Sadly, hundreds of idols are immersed without bothering about environmental threats. The authorities should create awareness of the need to immerse the idols elsewhere to save the river from more pollution," he said.

A report released by the international NGO Worldwide Fund for Nature (WWF) two years ago said the Ganges was among the 10 big rivers in the world facing extinction.

The Ganges has also shifted its natural course near Patna. It now flows over two kilometres away from the city due to the pollution.