The Mississippi River has peaked at 14.6 metres (almost 14 feet) in the city of Memphis in the the southern United States.
Flood levels there are at the highest since the 1930s, forcing people from about 1300 homes.
More than 300 people were staying in shelters on Monday.
The record river height of 48.7ft was set in February 1937.
The Memphis Commercial Appeal newspaper reported on Monday that the Mississippi was three miles (4.8km) wide in central Memphis. Its typical width was half a mile.
Officials say they are confident flood control systems will prevent further harm, but warn it could take weeks for the floodwater to recede.
The flooding has been caused by melting snow and heavy rains.
''It's not going to get a lot better for a while,'' said Tennessee Governor Bill Haslam.
The BBC reports the Mississippi has already caused significant flooding upstream in Illinois and Missouri.
It is also at flood stage further downstream in Arkansas, Mississippi and Louisiana.
In Louisiana, the Coast Guard has opened flood gates outside New Orleans to help protect the low-lying city.
