India’s special environmental court has criticised the government for its failure to curb river pollution, a lawyer petitioning the court has said, after scores of bodies surfaced in the Ganges river.

Last week more than 80 bodies – mostly decomposed skeletons and half-burned corpses – surfaced in the river in the northern state of Uttar Pradesh after a drop in water levels.

Their emergence has reignited concerns among environmentalists over the uncontrolled practice of body disposal in the Ganges by Hindus, who consider the river to be sacred.

On Monday the National Green Tribunal (NGT), a court set up to look at environmental grievances, ordered both the water resources and environment ministries to explain who should be held responsible for the pollution in the Ganges.

“The court said that it was really very unfortunate that the pollution levels are increasing and told the central government to do something about it,” said Gaurav Bansal, a lawyer representing a group of environmentalists petitioning the NGT. “The government has to reply by 27 January.”

The 1,600 mile (2,500km) Ganges river, which originates in the Himalayas and spills out into the Bay of Bengal, is a means of livelihood for more than 400 million people, as well as being Hinduism’s holiest river.

Millions visit places along its banks, such as the sacred city of Varanasi, to cremate their dead and scatter their ashes in the river.

Others bathe in the Ganges in an act of ritual purification, believing the river cleanses them of sin and frees them from the cycle of rebirth.

Authorities say the corpses in the Ganges are the deceased from poor families who cannot afford to buy enough firewood for cremation and are forced to immerse the half-burned bodies of their loved ones in the river.

Unmarried women and children are often buried in shallow graves along the riverbank, and their remains can be washed into the river when water levels rise.

Bansal said at least 3,000 bodies were recovered from the Ganges annually, yet the government had remained a “mute spectator” to the health risks of cremations and burials along its banks.

The Ganges is considered to be the country’s most polluted river, tainted by industrial effluents, sewage and waste from human settlements built on its shores.

India’s prime minister, Narendra Modi, who represents a constituency in Varanasi, has pledged to clean up the river as part of a broader push to harness scarce water resources and improve public health.