It can happen:
LAKE DELHI, Iowa --
Images: Lake Delhi Dam Fails, Evacuations Ordered
Warning sirens were set off in the small eastern town of Hopkinton as water continued to flow through a dam on Lake Delhi.
The National Weather Service said the Lake Delhi dam has failed and small communities downstream could be severely flooded.
The lake, which is part of the Maquoketa River, has been rising in recent days because of torrential rains.
The dam is a concrete-constructed spillway with earthen structures on either side.
A 200 foot section is gone, rescue crews said. People said wrecked boats and propane tanks could be seen floating in the waters.
The town of Hopkinton has been evacuated. Flash flood warnings have been issued downstream.
Gov. Chet Culver has called in the National Guard and put the area in a disaster declaration.
Meteorologist Chris Legro told the Associated Press that water was detected flowing beneath the dam and a complete failure is possible.
Water continues to surround homes in Hopkinton and the floodwater was expected to make its way south to Monticello, where events at the Jones County Fair have been canceled because the river runs near the fairgrounds.
Early Sunday morning, a representative of the Lake Delhi Recreation Association told KCCI that evacuations were under way downstream of the dam.
"I've never seen anything like it," said Department of Natural Resources Environmental Specialist Tom McCarthy. "I've seen fully grown trees washed downstream in less than a minute."
Agents said the dam was last inspected by the DNR in May 2009.
McCarthy said that although minor repairs were needed, no major structural problems were found on the dam.
"There really isn't much that can be done when we get into an extreme situation like this where water overtops the structure. The water is just too strong to hold back at that point," said DNR Flood Plain and Dam Safety Section supervisor Lori McDaniel. "No matter how hard we may try, there are times when the forces of nature are just too much for manmade structures. That's why it is important that we be well prepared for emergency situations like this."
Officials were attempting to shore up weak spots but the dam continued to be threatened by high water.
They said the current water levels are higher than those in 2008."