CEDAR FALLS, Iowa -- Residents were ordered to evacuate low-lying sections of towns along the overflowing Cedar River on Wednesday, and communities along the Mississippi River were warned that new rainfall would boost their expected flood crests.

A new wave of rain showers spread across parts of Iowa on Wednesday, including some flood-threatened areas. The rain came as a band of storms rippled across the northern Plains.

A sandbagged levee prevented the Cedar River from flooding this northeastern Iowa city on Wednesday, but officials asked for extra volunteers to help shore it up. Just downstream along the Cedar River, the neighboring city of Waterloo ordered a mandatory evacuation of some neighborhoods, not because of the river but because the ground was saturated and pumping stations couldn't keep up, officials said.

To the southeast in Cedar Rapids, more than 200 residents of a neighborhood near the river were told to seek higher ground.

In Vinton, electricity was cut Wednesday morning when rising water affected the city's municipal power plant, said Steve Meyer, the assistant emergency operations center manager. He said a 15-block area near the river had already been evacuated.

"The water is at least 3 feet deep. It's still coming up," he said of the town, home of about 5,000 people between Cedar Falls and Cedar Rapids.

The Cedar River had been expected to top the Cedar Falls levee during the night and deluge the downtown area of the city of 35,000 people some 88 miles northeast of Des Moines. But city spokeswoman Susan Staudt said early Wednesday that the sandbags appeared to be holding.

Flood stage at Cedar Falls is 88 feet, and by about 5 a.m. the river stood at 101.8 feet, down slightly from earlier in the night. The previous record was 99.2 feet in 1999.

Thousands of volunteers who showed up Tuesday to help with the sandbagging effort "saved this city, but we are still at a critical point," Staudt said.

She said more volunteers were needed to help reinforce the sandbag wall, which rises several feet above the levee. Volunteers patrolling the sandbag wall during the night reinforced spots where water was seeping through, she said.

Greg Starbeck said Wednesday that he and his three daughters helped fill and stack sandbags until late Tuesday.

"Everybody is doing something, whether it's tying bags or getting water for other people," Starbeck said. His house was safe from flooding but water was 5 feet deep in a rental house he owns.

In Waterloo, fast-moving water swept away a railroad bridge used to transport tractors from a John Deere factory to Cedar Rapids. It also led the city to shut its downtown and close five bridges.

Along the Mississippi River, the National Weather Service has predicted crests of 10 feet above flood stage and higher over the next two weeks in the Missouri and Illinois stretch of the river. Most of the towns are protected by levees, but outlying areas could be flooded.

The river was 1.5 feet above flood stage Wednesday at St. Louis, on its way to 5.6 feet above, and the floating President Casino closed for the second time this year because of flooding on its riverfront access road.

With more heavy rain forecast upriver in Iowa, crests at Missouri's Mississippi River towns could be higher than currently forecast, said weather service hydrologist Jim Cramper.

"It's when the rain falls upstream that it's a bigger impact on you," Cramper said. "As this new batch of water comes down, the river could start creeping up again."

That reflects conditions that have existed all spring, said Susie Stoner, spokesman for Missouri's State Emergency Management Agency .

"We have rivers that have been at flood stage since March," Stoner said.

In Wisconsin, state and local officials were monitoring dams threatened by the high water from days of storms.

Wisconsin officials planned to let water out of the reservoir behind Primmer Dam, in the southwestern part of the state, to ease pressure on the weakening structure, said Russell Rasmussen of the Department of Natural Resources. He said a number of homes and a highway are located downstream from the dam.

"There's some seepage coming out," Rasmussen said. "We're concerned the dam is weakened to the point of becoming a problem."

As of Wednesday morning, Milwaukee had measured 9.21 inches of rain already this month -- including a record 7.18 inches in a 48-hour period -- and the June record is only 10.03 inches, set in 1917.

A levee failed early Wednesday in southwest Indiana near the town of Capehart, flooding several square miles of farm land near the White River, and Daviess County authorities urged residents to evacuate.

"We've got about a 40-yard swath of levee that's gone," said Indiana state Rep. Dave Crooks, speaking for the county's Emergency Management Agency. "We've got rapidly rising water in that whole bottom area."

Authorities also ordered as many as 300 residents north of nearby Maysville to evacuate late Tuesday after water topped a levee.

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Associated Press writers Amy Lorentzen in Cedar Falls, Iowa; Luke Meredith in Des Moines, Iowa; and Todd Richmond in Lake Delton, Wis.; and David N. Goodman in Detroit contributed to this report.