A holiday afternoon on the water turned deadly in southern Wisconsin on Friday, when a violent storm swept over Geneva Lake and overturned a boat full of people.

A storm off the water

The boat, carrying 10 people, capsized in Walworth County shortly after noon as a sudden, severe thunderstorm crossed the lake near Big Foot Beach, CBS News Chicago reported. The National Weather Service had issued a severe thunderstorm warning for the area, with wind gusts clocked around 70 mph. Three people died and seven were rescued from the water, and no one was left missing, NBC Chicago reported.

What officials said

Walworth County Undersheriff Tom Hausner confirmed the toll and said all three bodies were recovered. Some news outlets, citing a source, reported that the three who died were children; the undersheriff said he could not confirm those reports. Authorities have not released the identities of the victims, and the Herald is not naming them.

Hausner described a chaotic, large-scale response, with multiple people hurt and taken to hospitals, and said the strain on emergency crews was severe. The city of Lake Geneva declared a state of emergency, and the same storm downed trees and power lines and damaged buildings across the southern part of the county. The Geneva Lake Law Enforcement Agency and the Wisconsin Department of Natural Resources are investigating.

A danger that arrives fast

Summer thunderstorms can build in minutes and turn a calm lake violent, and holiday weekends put far more boats on the water. The Wisconsin DNR urges boaters to check the forecast before heading out and to wear a properly fitted life jacket at all times; the National Weather Service advises anyone on open water to get to shore immediately when a storm threatens, since a lake offers no shelter from lightning or high wind. Whether those killed Friday were wearing life jackets had not been stated by officials.

For a lake town in the middle of its busiest weekend of the year, the disaster was a sudden, wrenching turn — a reminder of how quickly the weather can change, and how little warning it can give.