The sacred river Ganges in India is one of the most enduring images of the country.

With its banks lined with holy men and devout Hindu pilgrims, the river flows inexorably from the mountains to the sea.

The source of the river is high up in the Himalayas

The waters are believed to have a healing or preservative effect.

Hindus believe that sins can be washed away by bathing in the Ganges.

Pilgrimage routes criss-cross these mountains, and the devout brave harsh conditions to do their religious duty.

No Himalayan pilgrimage is more important than the journey to the source of the Ganges.

A test of faith

Two days hard walking from the nearest road, remote, rugged - a place to let the cares of the world flow downstream with the sacred river.

The Ganges is sacred to many Indians

One pilgrim, known as Kalidas, said that people of all ages come - on foot.

"It is very important to walk," he says.

"While walking, the suffering that a person goes through individually will make that person transcend from the body level to the mind."

The BBC's Daniel Lak: "A place to let the cares of the world flow down stream with the sacred river"

In a wall of ice at the end of the Gangotri glacier the Ganges is born.

The icy waters are deeply sacred to many Indians, and here holy men bath away their sins and offer prayers, even as the ice crumbles above them.

Environmental damage

But concern is growing in India about environmental degradation and its effect on the sacred river.

That is the problem.

The Gangotri glacier where the Ganges is born

In recent years, the glacier has been retreating and the implications for India are frightening.

According to geologist Dr H C Nanwal, glaciers are the major source of India's fresh water.

"If they melt faster than they form, it means shortages and drought downstream," he says.

He adds: "We have to do something to stop this destruction."

In the past 50 years, the ice has been melting five times faster than before.

Sometime in the next millennium, the holy Ganges could dry up.

People problems

People are largely to blame.

Tourists and thousands of pilgrims travel the precarious mountain roads and trails to get here.

Deforestation and construction have taken its toll

Gangotri village, once a temple and a few simple places to stay is now an environmental nightmare - its famous waterfall a backdrop to overbuilding and deforestation.

Environmentalist Swami Sunderanand, says that when he first came to Gangotri, it was "heaven."

"Now they have made it hell," he says.

"They're building hotels everywhere and cutting down forests. It's polluting the river and causing the glacier to melt. I don't think it could get any worse."

As one of the holiest places in Hinduism, the human burden here won't get any lighter.

Tourism will grow too because India needs the money.