Umeme Limited said the floating weeds had appeared at Nalubaale and Kiira dams on the Nile River as it started its journey from Lake Victoria.
Uganda on Tuesday temporarily shut down two key hydropower plants in the eastern part of the country after a floating "island" of weeds moved toward the installations.
Umeme Limited, the country's main electricity distributor, said in a statement that the floating weeds had appeared at the Nalubaale and Kiira dams on the Nile River as it started its journey from Lake Victoria.
"The development is affecting supply in the Kampala Metropolitan and surrounding areas following emergency load shedding until the floating island has been cleared," Umeme added.
The two plants account for about 380 MW of the country's current generation capacity of more than 1,300 MW.
In 2020, Uganda experienced a nationwide power blackout after floating weeds affected the Nalubaale power plant, one of the leading hydropower stations in Uganda.