(Bloomberg) -- Water levels at the Kariba reservoir, southern Africa’s largest man-made dam, have dropped to a record low.

The dam had 5.63% of usable storage on Monday compared with 27% at the same time last year and less than the previous low set almost three decades ago, according to data available on the Zambezi River Authority’s website. Normally, water levels start rising in January. 

The agency manages the dam’s water supply for Zambia and Zimbabwe, which both rely on it for nearly half of their electricity generation. The plunging levels have resulted in water allocations for next year being cut by 11%. 

Zimbabwe’s state-owned power utility, the Zimbabwe Electricity Supply Authority, warned Sunday of an increase in nationwide power outages due to technical faults at its thermal-fired plants in Hwange and at Kariba. The utility said it’s “experiencing depressed electricity generation and as a result there is increased pressure on the grid.”

Kariba, which has a total installed capacity of 2,130 megawatts split between the two countries, was producing only 602 megawatts of power Tuesday on the Zimbabwean side.

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