A group of prominent Indian scientists and engineers has issued an urgent appeal to stop the building of a hydro-electricity project on the Ganges.
Their appeal came as noted scientist GD Aggarwala continued his 36-day fast against the project. He has been on a water and honey diet since 14 January.
Campaigners have called for the project to be halted before Dr Aggarwala dies.
They say underground tunnels for the dam will mean that at least 60km (37 miles) of the river will disappear.
The central government wants to build the 600 megawatt power project in the Bhagirathi valley.
But the engineers, environmentalists and scientists say the river will be irreparably harmed.
They say that the dam - planned to be built at the source of the river - threatens its natural flow. The environment will be severely damaged, they say.
Award winning environmentalist MC Mehta said the project would also rob the river of its cultural and religious significance.
"We are not against development, but we are for sustainable development. Once the prime minister has declared the Ganges as a national river, it should be protected and preserved as a national symbol. All construction or any exploitation of the river must stop," he said.
The speakers emphasised the cultural, spiritual and economic significance of the Ganges, which affects the livelihood of at least 450m people.
"Ganga ji (the Ganges) is no ordinary river. She has been at the core of our great and very ancient civilisation," campaigner Krishna Dhar said.
"And yet the Ganges is under threat like never before. Even the British when they built the Ganges canal in colonial times responded to public protests and agreed never to completely block the natural flow channel of the river.
"We in free India on the other hand seem to have no such compunction. Dams and tunnels have been built and are proposed to be built affecting the Ganges in ways that are not completely understood - threatening the survival of this perennial river."
The campaigners on Wednesday said that they had given a 25-point charter to the government, calling on it to protect the river.
The speakers called on the government not to construct any dams in the upper reaches of the Himalayas.
They said that efforts should be also made to stop municipal authorities from directly dumping polluted water into the river.
India's electricity needs have been growing rapidly along with its fast growing economy.
About a quarter of its power is provided from hydro-power plants.
The government says new dams currently under construction will go a long way towards meeting outstanding energy needs.