A supreme court order in India asking the government to link more than 30 rivers and divert waters to parched areas has sparked concerns in neighbouring countries.
Bangladesh says it would be hardest hit because it is a downstream country to two major rivers that flow from India.
New Delhi is yet to respond to the neighbouring countries' reactions.
The multi-billion-dollar project was announced by the Indian government in 2002 but had since remained on paper.
Experts in Nepal say the country's unstable political situation could open the door for India to build dams and reservoirs in Nepalese territory for the inter-linking project - known as the ILR.
Hydrologists say as an upstream country, Nepal has ideal locations for the infrastructure required to make the mammoth Indian project happen.
Bhutan too has similar locations and some of its rivers are tributaries to the Bramhaputra, a major river system in the region included in India's river-linking project.
Long-running disputesThe project's basic idea is to take water from areas where authorities believe it is abundant and divert it to areas where there is less available for irrigation, power and human consumption.
Official Indian documents have stated that the country - with its population of 1.2 billion - is increasingly water-stressed.
But when the government tried to present the ILR as a possible solution, it became quite controversial as critics argued it would have huge environmental consequences.
They also said it was unfeasible on technical grounds and that not all the states through which the rivers flow might allow waters to be diverted.
Some Indian states already have long-running water sharing disputes.
Delivering the court's order earlier this month, the judges said the project had long been delayed, resulting in an increase in cost.
Some 10 years ago, the super-ambitious scheme was billed at $120bn and was estimated that it would take 16 years to complete.
The court has also appointed a committee to plan and implement the project in a "time-bound manner".
Even before any of that began, Bangladesh was already quite critical of the idea.
"We can never agree to it," Ramesh Chandra Sen, Bangladeshi water resources minister told the BBC.
"Our agriculture, economy and our lives depend on these rivers, and we cannot imagine their waters being diverted."
Downstream impactsThe Ganges and the Bramhaputra, Asia's major river systems that flow down to Bangladesh, are among the rivers India has planned to divert to its western and southern parts.
Ainun Nishat, a Bangladeshi water resource expert, was even more critical.
"India assumes that these rivers stop at its borders and that there will be no downstream impacts to Bangladesh if it did anything to those resources," he said.
"They (India) have always thought that the Bramhaputra has a surplus water but they don't seem to remember that there is a sovereign country called Bangladesh downstream which has a need for water."
Minister Sen said there had been no official communication with his government on the project from the Indian side.
Nepal's Energy Minister Posta Bahadur Bogati too said he had not received any official information.
Senior Nepali water expert Santa Bahadur Pun said there were concerns that politicians might not be able to secure a good deal for allowing India to build dams and reservoirs in Nepalese territory.
"That is because we hear our leaders talking only about the stereotype hydropower development whereas they should be focusing on making India pay for the downstream benefits it would be getting from its river-linking infrastructures in Nepal."
Such concerns also stem from the fact that some think Nepalese politicians are too preoccupied with the prolonged peace process that India mediated after a 10-year Maoist insurgency.
Bhutan says it has not been apprised of the project idea.
"While we recognise rivers as a trans-boundary issue, there has been no direct dialogue as far as building structures in Bhutan for the project (of India) is concerned," Bhutanese Minister for Agriculture and Forests Pema Gyamtsho told the BBC.
'Conceptual stage'Media reports and academic papers apart, little has come out officially about the inter-river linking project.
In 2006, the Indian water resources minister at the time gave a brief response in the parliament when asked if there would be a white paper on the project.
"The ILR project is still at a conceptual stage only and all the far-reaching effects of the link projects can be analysed at the stage of preparation of detailed projects.
"As such, there is no need to release a white paper on the ILR at this stage."
Indian water resources ministry officials made no comment to the BBC's query how India took its neighbours' reactions to the recent supreme court's order to implement the river linking project.
Many of India's past water treaties and agreements with neighbouring countries Bangladesh, Nepal and Pakistan have been mired in disputes.
And now New Delhi has had to worry about China's plans to divert its southern rivers to the north, analysts say.
The main concern has been proposed Chinese hydro-electric plants on Tibet's Yarlung-Tsampo river that becomes the Bramhaputra in India, although Beijing has said it does not intend to divert its waters.
A number of studies have shown South Asia as one of the flashpoints over water resources in the future, particularly in the wake of climate change and a burgeoning population.
A recent assessment by the US intelligence agencies has said beyond 2022, South Asia will be one of the regions in the world where "water would be used as a weapon of war or a tool of terrorism".
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