Iran has struggled to invest the pledged amount into the project due to ongoing sanctions against its government said the Mahaweli Development and Environment Ministry Secretary, Nihal Rupasainghe.
Rupasinghe added that Sri Lanka would not be able to provide extra investment for the short-fall as requested by Iran.
The Uma Oya Multi-Purpose Development Project includes a series of damns, a hydropower plant with a 134 MW capacity, and a tunnel system that will carry water to the southern city of Hambantota.
The $529 million project was financed with a $450 loan from the Export Development Bank of Iran.