The National Emergency Management Agency (NEMA) said it had been informed that the Lagdo dam in northern Cameroon would be emptying water into the River Benue until November to relieve an excessive build-up.
The opening of the dam as well as heavy rain in 2012 led to huge flooding along the river, the main waterway in eastern and central Nigeria.
Authorities in northeastern Adamawa state said at least 30 people had been killed and 120,000 displaced, while more than a dozen Cameroonians were reported to have died.
NEMA warned populations along the river to be on alert and “ready for evacuation” in case of a possible repeat.
It urged local authorities and emergency agencies along the 1,400-kilometre (870-mile) river, the main tributary of the River Niger, to prepare safe locations to move affected communities.
The 300-metre (985-feet) Lagdo dam, 50 kilometres south of the Cameroonian city of Garoua, was completed in 1982 and supplies electricity to the country’s north.