Local officials in northern Nigeria say two million people have been displaced after the authorities opened floodgates on two dams.
Torrential waters have swept through plains and low-lying areas of Jigawa, a region bordering the Sahara.
Local government officials say that two million people are homeless, up to 5,000 communities affected and farms, property and livestock destroyed.
They say that officials in a neighbouring state decided to open floodgates on the swollen Challawa and Tiga dams because of fears that they might overflow.
The spokesman for the Jigawa state governor criticised those officials responsible, saying they released water indiscriminately.
Settlements are now being evacuated and families moved to higher ground.