Experts have blamed the run-off from the coal mines in Meghalaya's Jaintia Hills district for the acidic water in the reservoirs of Assam's Kopili Hydro-Electric Project. There has been a rise in the acidity level of the dam waters that is threatening to hit functioning of the 275 MW project, commissioned in 1984.

Besides, the experts also said that this phenomenon of water turning acidic in the reservoirs is the first such in the country.

"This is a unique problem and has happened for the first time in the country," Director of the Central Soil D Material Research Station Murali Ratnam said.

Ratnam, however, insisted that the situation was not 'alarming' and can be controlled. "Though there have been damages to certain hydraulic structures and machines, there is no harm to the concrete structure of the dam," he said.

The water was first found to be acidic in 2006 and since then the acidity level has been rising. A study by Geological Survey of India found that geological formations, human activity, effect of pollution were some of the possible causes, a spokesman of North Eastern Electric Power Corporation Ltd (NEEPCO) said.

Dubbing the problem as a national one, CMD of NEEPCO, IP Barooah said efforts are needed to save the project which has been one of the most economic projects in the country.

"Even now, the cost of power generation in the Kopili project is about 70 paise per unit. Whereas, nowadays the cost of production in new projects tends to be Rs 2 to Rs 3," Barooah said.

Power generation at the plant, located in Assam's North Cachar Hills district, adjacent to the coal mines of Meghalaya, has been badly affected due to unprecedented rise in wear and tear and breakdown of machines and hydraulic structures caused by the acidic waters.

"The frequency of replacement of some equipment has increased considerably over the last two years," he said.