India's holiest river is also one of the world's fastest shrinking rivers, a study has revealed.

The Ganges has at least 20% less water flowing in it than it did in the 1950s and could dry up in another 50 years.

The 1,500-mile river, the country's most culturally and economically important, ranked among 45 rivers worldwide in the US study that showed a significant drop in discharge to the ocean.

The study, conducted by the National Centre for Atmosphere Research in Colorado, indicated that the Ganges could shrink even faster in the next few decades.

The Hindu holy river is losing its volume of water as the Himalayan glaciers that feed it lose their mass.

A 2007 UN Climate Report had indicated that the glaciers themselves may disappear by 2030, after which the flow would be reduced to a seasonal occurrence resulting from the monsoons.

This too is a matter of concern as the new study has revealed that rainfall to the area has diminished over the past five years. The atmosphere above the Indian Ocean has become warmer resulting in a weak south-west monsoon which replenishes the country's water supply.

Kalyan Rudra, a noted river geologist, told Indian newspaper the Hindustan Times that the Ganges also faces the problem of indiscriminate irrigation.

The river and its tributaries reportedly drain a 390,000 sq mile fertile basin across northern India that supports one of the world's highest densities of human population with close to 400 million people living near it.

Hindus believe that bathing in the holy waters will help wash their sins away, and because of this they conduct repeated ritualistic washings in the river to secure a place in heaven.

The study revealed other rivers that showed a reduction in discharge to the ocean including North America's Columbia, Africa's Congo and Niger, United States' Mississippi, Russia's Yenisey, and South America's Parana and Uruguay.