Tens of thousands of activists, protesting against the construction of a huge dam in the western Indian state of Gujarat, have set off on a journey to the construction site.

The protest is one of the several led by activists in the last 15 years.

The Narmada project dates back to the 1940s. It was part of a vision of development articulated by India's first Prime Minister, Jawaharlal Nehru.

Several legal and logistical arguments between various Indian states over the project delayed progress until 1979.

Ambitious undertaking

Apart from the Sardar Sarovar project on the eastern edge of Gujarat state, another huge dam called the Narmada Sagar is to be built in the central Indian state of Madhya Pradesh.

A massive undertaking

In addition, at least 30 large dams, 135 medium ones and nearly 3,000 small dams, used to channel water into thousands of miles of irrigation canals, are to be built.

Since its inception, the project has faced several economic and legal obstacles.

Environmentalists argue this will mean that eventually only 35% of the river will flow in to the Arabian sea.

If completed, the Sardar Sarovar dam will be about 450 feet high, submerge nearly 40,000 hectares of land and displace a quarter of a million people.

Those who argue in the project's favour say it will supply water to 30 million people, and irrigate crops to feed another 20 million.

They say land which would be submerged by the waters of the dam is already greatly degraded and deforested. They also point out that hydroelectric power is cheaper and less polluting than thermo-nuclear power.

Environmental costs

But anti-dam activists criticise the claims. Environmentalists have lobbied hard in the past decade to prevent large dams being built.

Construction has carried on for 15 years

The dams, they say, will submerge forest farmland, disrupt downstream fisheries and possibly inundate and salinate land along the canals, increasing the prospect of insect-borne diseases.

One of the most contentious issues has been the displacement of up to a quarter of a million people, many of whom belong to small tribal communities.

Much of the debate has also centred around the propriety of building large dams when smaller dams might do. Some scientists say the construction of big dams could cause earthquakes and, in a country as disorganised as India, it is likely that necessary maintenance of these dams may suffer.

World Bank withdraws

There have been several protests against the project organised under a coalition called the Narmada Bachao Andolan (Save the Narmada Movement).

Environmental and human concerns have also led to international lending institutions pulling out of the project.

The World Bank withdrew from the project six years ago, in a move that was seen as a breakthrough by anti-dam activists.

But now, many believe the project is unlikely to be abandoned. More than 20bn rupees have already been spent and the government argues that stopping the project half-way would be wasteful.