The news will be a breath of fresh air to India's 830 million Hindus, each of whom must bathe in holy waters of the Ganges at least once in their lifetime.

According to Hindu scripture, the river was created from the hair of the god Shiva to purify the earth and wash away its sins.

Today the government is banking on new sewerage treatment plants to purify the "cleansing river" which is slowly dying under the weight of billions of litres of excrement, chemical waste, ashes and the bloated bodies of dead humans and animals.

The stench from the treacle-like Ganges – or Ganga – has become a talking point among tourists who visit the holy city of Varanasi to marvel at the devotion of Hindus who drink its black water.

It is a source of embarrassment to ministers who would like to see one of the country's greatest attractions returned to its former glory.

Environment minister Jairam Ramesh unveiled "Mission Clean Ganga" to create new water treatment plants, reduce human and chemical pollution and bring sewage levels down towards bathing standard by 2020.

The government has applied for a £1.5 billion World Bank loan to finance the project but has pledged central and state government funding to underwrite the work.

Treatment plants in northern Indian cities which line the Ganges, like Kanpur, Lucknow and Allahabad, currently have the capacity to clean 220 million gallons per day of the 660 million gallons of sewage per day the towns flush into the river.

However, experts said they do not believe the plan will succeed because it does not include the funds needed to move the sewage to the new treatment plants, or pay for the 24-hour electricity supply they need.

RK Srinivasan, of the Delhi-based Centre for Environment and Science, said similar action plans had wasted hundreds of millions of pounds on failed projects to revive the Ganges' tributary, the Yamuna River.

He said while Delhi has 30 sewerage plants, only half the city is served by sewerage pipes, and 50 per cent of the city's raw sewage flows straight into the river. For the Ganges, only 15 per cent of sewerage is treated before flowing into the river.

Unpaid electricity bills mean many treatment plants sit idle, he said, while the sewage content of the rivers is concentrated because fresh water further upstream is diverted into the cities for drinking.

"People defecate in the river because although there are toilets – 85 per cent in cities and 26 per cent in rural areas have access to toilets – they are not in use because there is no maintenance and there is a lack of water," he said.

"The government should focus on managing the water, let fresh water flow in the river. Then the Ganga's sewage would be diluted," he said.