The company, which started the process of filling up of the reservoir, could not complete the exercise as the reservoir was unable to hold water for the project.
According to company sources, the work will be delayed and the project commissioning may be postponed by at least an year from its earlier schedule of April 2014.
"This may amount to a loss of Rs 150 crore to Himachal Pradesh government," the source said.
Started in 2003, the project will have a cost over-run of about 20 per cent. The approved investment of the plant was Rs 4,527 crore.
It has been delayed mainly due to environment and geological hurdles. The project was earlier slated for commissioning in 2009.
The project will supply electricity to Delhi, Haryana, Punjab, Rajasthan, Uttar Pradesh, Himachal Pradesh, Jammu & Kashmir and Chandigarh.
Koldam has an installed capacity of 800 MW, comprising four units of 200 MW each.
The company is also executing three more hydel plants - Tapovan Vishnugad (520 MW) and Lata Tapovan (171 MW) in Uttarakhand and Singrauli Small Hydro Project (8 MW) in Uttar Pradesh.
At present, NTPC generates 43,019 MW of electricity and plans to add 14,000 MW in the current plan period (2012-17).