The governor of Iowa sent helicopters to a small town to evacuate people from flooded homes Saturday, the result of weeks of rain, while much of the United States longed for relief from yet another round of extraordinary heat.

Sirens blared at 2 a.m. in Rock Valley, Iowa, population 4,200, where people in hundreds of homes were told to get out as the Rock River could no longer take rain that has slammed the region. The city lacked running water because wells were unusable.

“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,” Mayor Kevin Van Otterloo said.

“We’ve had so much rain here,” he said. “We had four inches last night in an hour and a half time. Our ground just cannot take anymore.”

Gov. Kim Reynolds declared a disaster for Sioux County, which includes Rock Valley. Drone video posted by the local sheriff showed no streets, just roofs and the tops of trees above water.

Elsewhere in the U.S., the miserable grip of heat and humidity continued. The National Weather Service said roughly 15 million people were under a heat warning — the highest warning — while another 90 million were under a heat advisory.

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Temperatures around 100 degrees Fahrenheit (37.8 degrees Celsius) were predicted for Washington, D.C., and Richmond, Virginia — while Philadelphia; Newark, New Jersey; Columbus, Ohio; and Detroit were bracing for the high 90s.

Heat-related hospital visits in New York state were 500% higher than the average June day, according to the Department of Health.

“We still have this prolonged heat wave across portions of the Ohio Valley and into the Northeast,” weather service meteorologist Marc Chenard said. “We get a little bit of relief by early in the week, at least in the eastern U.S., the Northeast, but in general above-normal temperatures are going to cover a large portion of the country even into next week.”

In southeastern Michigan, DTE Energy said 8,300 customers still lacked power Saturday morning from storm-related outages, compared to 75,000 homes and businesses earlier in the week.

Flooding from rain was South Dakota’s problem. Several highways were closed, including a key stretch of Interstate 29, south of Sioux Falls, where there were no alternate routes. Sioux Falls, the state’s largest city, had more than 7 inches (17.7 centimeters) of rain in three days.

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AP reporters John Hanna in Topeka, Kansas, and Julie Walker in New York City, contributed to this story.