Days of heavy rainfall have pushed rivers to record levels across northwest Iowa, shutting down utilities in several cities and forcing evacuations.

Gov. Kim Reynolds issued a disaster declaration Saturday for 21 counties in the region, and the Iowa State Patrol and Iowa 511 warned against travel there because of flooded roads.

The most dramatic situation may have been in Rock Valley, where as much as 15 inches of upstream rain over the previous 72 hours sent the Rock River surging to a record depth of more than 27 feet. That was 5 feet over the previous record and 8 feet above major flood stage, 19 feet, according to the National Water Prediction Service.

A levee failed and the city sounded warning sirens early Saturday, telling residents north of Highway 18 to evacuate. State troopers blocked roads into the city to all but local residents, and the city said on its Facebook page that people were being brought out by boat because "the water current and height" had rendered the use of vehicles impossible.

KCAU-TV in Sioux City quoted Mayor Kevin Van Otterloo as saying aerial rescues also were underway.

"We've got National Guard helicopters coming in where people are on their roofs — literally on their roofs or the second floor because their first floor is completely flooded," Otterloo said.

The Sioux County sheriff's Facebook page said evacuations also were underway in Hawarden on the Big Sioux River, which likewise experienced record flooding. The city of Akron, just downstream, was warning residents to prepare to leave. And the National Weather Service in Sioux Falls, South Dakota, posted a storm watcher report of some evacuations in Spencer.

In Rock Valley and other cities across the region, the high water backed up sewage systems, and residents were asked to cease using water until service could be restored. Some areas also reported power outages.

Gov. Kim Reynolds said the Iowa Emergency Operations Center had opened to deal with the flooding, which also was reported in Sioux City, Sioux Center, Hull, Sanborn, Spirit Lake and Arnolds Park, according to the National Weather Service.

River managers were struggling to contain the flooding, which also affected southeastern South Dakota and southwestern Minnesota.

"In response to the rainfall, which has exceeded 600% of normal over the past 24 hours, we will lower releases today at Fort Randall and Gavins Point dams," said John Remus, chief of the Missouri River Basin Water Management Division. "While the decreased releases are expected to bring lower downstream river stages, they cannot offset all the flooding in the Sioux City area."

Wind and hail damage from storms Friday also was reported.

Here are the 21 counties covered by Gov. Kim Reynolds' disaster proclamation

Reynold's disaster proclamation in Iowa covers Buena Vista, Cerro Gordo, Cherokee, Clay, Dickinson, Emmet, Floyd, Hancock, Humboldt, Kossuth, Lyon, O'Brien, Osceola, Plymouth, Pocahontas, Sioux, Webster, Winnebago, Woodbury, Worth and Wright counties. It enables authorities to use state resources and activates assistance programs for affected residents, with grants of up to $5,000.

In a statement, U.S. Rep. Randy Feenstra, a Hull resident, said he was talking to Reynolds "and we are working with our local, state, and federal partners to deliver relief to our communities in Sioux County and Northwest Iowa. We will do everything possible to help our neighbors rebuild and recover."

More flooding to come as water flows south

As the excess water surges down Iowa rivers, other communities can expect to see flooding. The National Water Prediction Service shows the Cedar River hitting major flood stage Sunday in Charles City, Monday in Cedar Falls and Thursday in Cedar Rapids.

The West Fork of the Des Moines River is at major flood stage in Estherville and is expected to peak near its record level Tuesday, then exceed its record at Humboldt on Wednesday. The main channel of the river is forecast to reach major flood stage Wednesday in Fort Dodge.

So far, though, no flooding on the river is forecast in Des Moines, which is protected by the Saylorville Lake reservoir upstream.

One bit of good news: The National Weather Service in Sioux Falls, which issues forecasts for the region, said Saturday that the worst of the rain was past.

"Conditions will quiet down through the upcoming weekend into early next week," it said in forecast guidance.

The Sioux Falls Argus Leader contributed to this article.