The National Weather Service says the Lake Delhi dam in eastern Iowa has failed and several small communities downstream could be severely flooded.
Meteorologist Chris Legro says water has been detected flowing beneath the dam and a complete failure is possible.
Legro says about half of Hopkinton, a city of about 700, could be flooded. He says flooding also is likely later Saturday in Monticello, a city of about 3,600 people.
People who live in the Freddy’s Beach resort area around the lake are removing their belongings from flooded homes and evacuating.
Lake Delhi was created in the 1920s by damming the Maquoketa River. The area about 180 miles northeast of Des Moines is a weekend retreat with about 900 residents.