India's most important river, the Ganges, is to undergo a massive clean-up this week in the run up to World Water Day on 22 March.
By Jill McGivering
BBC correspondent in Delhi
It is an attempt to focus attention on the plight of India's rivers, many of which have deteriorated dramatically in recent years.
It is almost impossible to get clothes clean
Contamination from untreated sewage has made some rivers a health hazard - and the water unfit to use even for washing.
On the banks of Delhi's Yamuna, a laundry worker sings as he scrubs washing.
He is working with passion - but it is hard to imagine the sheets and shirts coming out any cleaner.
"20 years ago, they used to drink the river water," he told me. "Now it is so filthy, they can not even bathe in it."
The other workers agreed. One woman told me that when they washed the clothes, they had to use a lot of bleach or they came out black.
"We can't use any of the wells round here. We have water delivered by tanker. All the rest is contaminated," said one laundry worker.
This is supposed to be only to collect rainwater and it's become an open sewer
Centre for Science and Environment
As I walk towards the river bank I am hit by the smell.
It is a rotten sour stink coming up from the water - water that is just black in colour.
Rubbish floats along the edges of the river and there is thick smoke rising from a series of big rubbish dumps strewn along the opposite bank.
In cities like Delhi, about 80% of river pollution comes from untreated sewage.
The combination of fast growing populations and mostly old, poorly maintained sewage systems has proved lethal. The sewage from many homes is not treated at all.
Manoj Nodkarni of the Centre for Science and Environment showed me storm drains in the city, which have become unofficial sewage channels.
"This is supposed to be only to collect rainwater and it's become an open sewer," he said.
The Ganges is India's most important river
And he says the pollution hits India's most powerless the hardest.
"People who are actually suffering from this don't really have a voice. It's the people downstream who suffer, the poorer people, the fishermen, the people who are falling sick," said Manoj.
"We do so much for Aids and cancer and cardiac problems but the biggest killer in India is still water-borne diseases and these are preventable deaths."
The government is spending vast sums of money on tackling river pollution.
RP Sharma of the Ministry of the Environment and Forests says a plan to clean up the Ganges - or Ganga - started 18 years ago.
It has reduced pollution but by less than a third.
"Ganga river is ten times longer river than the River Thames in the UK, we have shortage of resources as well in our country so it is going to take some time and it's not one river alone, we're doing 29 rivers now," says Mr Sharma.
It is little comfort to fisherman Bhopal Singh. We met him while he was packing away nets after a long morning's fishing. All he caught today was one small fish.
"Ten years ago I used to catch up to 10 kilogrammes of fish a day," says Mr Singh. "Now the nets come back empty. It's so dirty, there are no fish left."
Environmentalists in the UK are trying to help with advice and shows of support.
Theo Rhys Thomas of the Thames 21 action group has just arrived to join a clean up campaign.
He says the key is getting pollution onto the political agenda.
"Governments only respond to public pressure - If we want to see rivers in India improve and pollution reduced, we have to make sure it's put up the political agenda," says Mr Thomas.
Further down the bank, priests and mourners carry out a cremation.
The river is also a final resting place.
Traditionally it plays a part in every Indian life, from the spiritual to the practical.
But without dramatic action, its own life is under threat.