CEDAR FALLS, Iowa — A sandbagged levee was preventing a swollen river from spilling over its banks and flooding a northeastern Iowa city, but officials on Wednesday asked for additional volunteers to help shore it up as more rain loomed.

The Cedar River had been expected to top the levee during the night, deluging downtown Cedar Falls, a city of 35,000 people some 130 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.

Thunderstorms arrived in western Iowa during the morning as a band of storms rippled across the northern Plains, and the National Weather Service issue a severe thunderstorm watch for northwest Iowa and parts of Minnesota and South Dakota.

"If we get more rain (the river) can rise again," Staudt said. "The levee and the ground is saturated and we want to make sure it doesn't give way."

Rising rivers wiped out a railroad bridge elsewhere in Iowa on Tuesday, closed part of a Wisconsin freeway and forced residents along the Mississippi River to prepare for what could be the worst flooding in 15 years.

In Cedar Falls, Donita Krueger was among those helping fill sandbags Tuesday.

"If this breaks, the whole downtown will be flooded," she said. "Everything goes on down here. It would be a big hit to the community."

White, yellow and orange sandbags lined downtown, which was evacuated Tuesday. Tarps and plastic were taped to windows and doors. Mary Dooley of the American Red Cross said more than 70 people stayed in a shelter overnight.

In nearby 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.

To the south, municipal officials in Palo urged residents to evacuate as water was expected to rise as much as 2 feet higher than in 1993, when devastating flooding covered wide areas of Iowa and adjoining states.

Flooding threatened water treatment plants in several towns, Lt. Gov. Patty Judge said. Mason City's plant was knocked out of service Sunday when the Winnebago River broke through a levee, while officials in Des Moines hoped that releasing water from the Saylorville Reservoir would protect the capital city and its water treatment plant.

In Wisconsin, fixing the broken and nearly empty Lake Delton, where water carved a new channel as it rushed through a huge gap in an embankment, was only one of the challenges facing engineers and contractors on Wednesday.

The rising Rock River near Johnson Creek threatened a bridge and shut down westbound lanes of Interstate 94, which links Milwaukee and Madison.

State and local officials were monitoring various dams where high water from days of storms threatened to make them give way.

But while the new storms moving across the Midwest on Wednesday threatened to drop an extra inch or two of rain on Wisconsin on Thursday, weather service meteorologist Bill Borghoff said a dry spell could be coming.

"As we head into next week, it looks pretty dry for the most part," he said.

In Elnora, Ind., about 100 miles southwest of Indianapolis, berms of white sandbags and concrete barriers held back the White River. Most residents left after voluntary evacuation orders came late Monday, two days after the area got up to 10 inches of rain.

Downriver from Elnora, a levee failed early Wednesday near the town of Capehart, 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. If you've got a home there, it's pretty serious."

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

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

"This is major flooding," weather service hydrologist Karl Sieczynski said of the Mississippi. He urged people in unprotected flood plain areas to seek higher ground.

Elsewhere, thunderstorms brought relief to parts of the East Coast that had been baking in a heat wave for four days. Temperatures in the upper 90s on Tuesday stretched from Georgia all the way to northern New England, where the weather service reported an afternoon high of 99 at Portsmouth, N.H.

The storms also knocked out power to hundreds of thousands of homes and businesses. About 93,000 customers in New Jersey, 110,000 in southeastern Pennsylvania, 75,000 in upstate New York and 20,000 in Connecticut remained without electricity early Wednesday, and some 152,000 customers were still blacked out in Michigan from a series of storms that began Friday.

Philadelphia officials blamed two deaths on the heat and the upstate New York storms were blamed for one death.

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.