(CNN) -- A dam on an eastern Iowa lake suffered a "catastrophic" failure Saturday, sending a massive amount of water into nearby communities and forcing residents to flee, officials said.

The Lake Delhi dam, about 45 miles north of Cedar Rapids, failed as a result of "massive rain -- a very unusually high amount this season," according to Jim Flansburg, communications director for Gov. Chet Culver.

Culver told CNN that nearly 10 inches of rain had recently fallen in a 12-hour period in the area and was "too much water for the dam to hold."

The roads on either side of the dam -- which were part of the cement dam's containment measures -- apparently gave out as a result of the rainfall, Flansburg told CNN.

The National Weather Service reported a 30-foot-wide gap in the berm alongside the dam.

Video showed massive amounts of water violently gushing from the pool behind the dam into the Maquoketa River below. Nearby homes and buildings were under water up to their eaves.

However, as of Saturday evening, the waters appeared to be receding, Flansburg said.

Much of the flooding occurred in farm areas instead of well-populated neighborhoods, Flansburg said, adding a would-be catastrophe was avoided.

Earlier Saturday, residents in Hopkinton, a town of about 700, were given minutes to flee approaching floodwaters, Flansburg said.

No injuries were reported.

The town of Monticello, where Culver was meeting with emergency personnel, was also under a flood warning.

Amanda Duck, a trained weather spotter along with her husband in Monticello, told CNN she had been watching the water slowly rise all day.

By evening, water was beginning to seep over a road that runs behind her house and into her neighbor's yard, she said.

"We're both just in a state of shock," Duck said. "We're just trying to keep our wits about us and help our neighbors."

Culver activated the National Guard in the area to help with recovery efforts, his office said.

He also issued disaster proclamations for Delaware and Jones counties due to the flooding.

Culver credited the lack of injuries to local officials providing early warning to residents in the flood plain about the possibility of a dam breach.

The governor said such a failure had never happened before.