The volume has fallen by 46% to 11.1Bm3 compared to last year's storage at this time of approximately 20Bm3.
Significant dam construction activity is continuing in the country, the Ministry added. It said that some 90 dams are being built at present.
Earlier this year the Ministry reportd that fewer dams had been completed in the Iranian year ending 20 March due to combinations of poor weather, limited materials supplies and financial support.
