The Indian prime minister says heavy rains have caused a "national calamity" in the northern state of Bihar.
They happened after heavy rain caused the Kosi river to burst its banks, sending huge waves of water out onto the land.
India has a rainy season every year, but these floods are thought to be the worst in more than 50 years.
Fifty-five people have died, and two million people have been left homeless...
At least 90,000 people have been rescued.
But many thousands are thought to be still stranded.
And fields of crops have been destroyed.
People now have to use boats to get around.
The Indian government has announced millions of pounds in aid, and people are being moved to temporary shelters.
But more rain is expected, and there are fears that more people could die.