Rainfall for the season, which runs from May to October, is about 40 per cent less than last year in the Central Highlands region.
The Pleikrong power plant in Kon Tum Province has been running for only one or two hours a day to reserve its meagre supplies.
And there have been days when it has had to cease operations altogether, said Dinh Van Hau, the plant's hydrographer.
The water level at the plant's reservoir is 10m lower than the average - and just a little higher than the critical level.
The water level at the Yaly hydropower plant in Gia Lai Province is just 4m higher than the critical level.
The plant's two reservoirs are usually full of water at this time of the year, said Yaly Hydropower Company's director, Ta Van Luan.
Total water flowing into the reservoirs is 100cu.m per second, but the plant's four turbines needs 104cu.m per second to generate their 180MW full capacity.
This year, the Yaly plant is expected to generate 800 million kWh, about 72 per cent of the amount planned.
Director of Tri An hydropower plant in southern Dong Nai province, Nguyen Kim Phuc, said water flowing into the plant's reservoir was only about 20 per cent of last year's amount.
Total generation this year is expected to fall by up to 800 million kWh.
"Even if there is rain in the next few months, shortages are unavoidable for the next dry season," he said.