At least 250 people have been evacuated from their homes in South Yorkshire because of fears that a dam could burst.
Council officials say engineers have found that Ulley Dam in Rotherham is in danger of bursting as a result of the heavy rains affecting much of the north of England.
At least three people have died and hundreds remain trapped by the flood waters that have devastated many areas.
Police searching for a 13-year-old boy swept away in the River Sheaf in Sheffield have confirmed that they have found a body.
He had fallen into the water near a playground at 5:15pm in the Millhouses Park area of the city.
A 68-year-old man has also been killed in Sheffield as he tried to cross a flooded road.
In Hull a 28-year-old man died after becoming trapped in a drain he was mending, despite a three-hour operation to try to free him.
Emergency services are mounting a major rescue operation overnight for hundreds of people who have become trapped in their workplaces by rising flood waters in Sheffield.
Around 35,000 homes are without power and hospitals in the city have appealed for staff to try to go into work to help out.
People stranded inside buildings told Sky News how they had watched helplessly as walls were pulled down and cars swept away by torrents of water raging outside.
Police said 25 people were trapped inside their cars on Brightside Lane.