Bodies recovered from India's Ganges
Reports said the bodies were of people who were dumped in the river or buried on the banks after their families could not afford a proper cremation.
Many Indians regard the Ganges as holy and use its bank for cremations.
The 2,500km (1,500-mile) river has been badly polluted by industrial waste, farm pesticides and sewage.
Prime Minister Narendra Modi vowed to clean up the river after his election victory last year.
Bodies were first found floating near the banks of the river on Tuesday in Uttar Pradesh's Unnao district.
Villagers noticed the bodies when many had become stuck on the river bank with dogs and vultures circling the area.
More were found on Wednesday, and authorities said so far 104 bodies had been retrieved.
"It seems that as the water level has receded in the river, these bodies have surfaced," news agency AFP quoted district magistrate Saumya Agarwal as saying.
"We are trying to figure out the reason. We have sent a team of doctors on the spot to collect the samples from bodies to investigate the case."
The BBC's Geeta Pandey in Delhi says bodies can regularly be seen floating in the Ganges, but this is a rare instance when so many bodies have turned up in one place.
Many Hindus do not cremate unwed girls and young boys, and many poor people cannot afford cremation so they wrap the body in white muslin and float it in the river, out correspondent adds.
Activists say the discovery of so many rotting bodies in one place can be a serious health hazard.
A multi-billion dollar initiative to clean up the polluted river over the years has largely failed, environmentalists say.
They say the river supports more than 400 million people, and if the unabated pollution is not controlled, it will be the end of communities living along the banks.