Hindus across India celebrate various religious festivals in September and October, paying homage to deities like Lord Ganesha, the remover of obstacles, and Goddess Durga, the destroyer of evil.

Elaborately painted and decorated idols are worshipped before they are taken during mass processions to rivers, lakes and the sea, where they are immersed in accordance with Hindu faith.

Environmentalists say the idols are often made from non-biodegradable materials such as plastic, cement and plaster of Paris and painted with toxic dyes.

After the statues are immersed, the toxins then contaminate food crops when villagers use the polluted water for irrigation, said Shyam Asolekar, science and engineering head at the Indian Institute of Technology in Mumbai.

"Even small traces are extremely toxic as they persist in the body for a long time and accumulate in the human tissues," said Asolekar, who has closely studied the effects of Hindu customs.

Paints contain metals like mercury, cadmium and lead, which can pass up the food chain from fish to human beings, he said.

Environmentalists said materials like plaster of Paris do not dissolve easily and reduce the oxygen level in the water, resulting in the deaths of fish and other aquatic organisms.

Statue remains from festivities last year still float in rivers and water tanks in Mumbai, where the annual "Ganesh Chaturthi" festival culminate in the immersion of some 160,000 statutes -- some up to 25 feet high -- by millions of devotees.

Traditionally, idols were made from mud and clay and vegetable-based dyes were used to paint them.

But commercialization of festivals such as Ganesh Chaturthi and Durga Puja has meant people want bigger and brighter idols and are no longer happy with the eco-friendly statues.

Authorities say they are taking steps to check pollution. Mumbai has dug 48 ponds this year for the immersion of idols, but environmental groups say not enough is being done.

"If we do not respect nature then we are not respecting god," said Manisha Gutman of environmental group Eco Exist.

About 80 percent of India's 1.1 billion population are Hindus. In recent years, their religious festivals and customs have come under increasing scrutiny as public awareness of environmental issues grows.