The two were swimming near a private dock in the lake when they were killed, according to a press release from the Missouri State Highway Patrol.

“The children screamed when the initial shock hit and when the adults dove in (to attempt rescue) they could feel the electricity in the water,” said Highway Patrol Sgt. Paul Reinsch. Then the adults turned off the electricity to the dock” before pulling the siblings out of the water and attempting CPR, Reinsch said.

The children, who were from Ashland, Missouri, about 60 miles north of the scene of the accident, were taken to Lake Regional Hospital, where they were pronounced dead.

Reinsch told CNN the water was electrified because of “a problem with the wiring going to the dock from the house,” although he stressed that investigators could not pinpoint which of several electrical components on the dock caused the accident.

The Missouri State Highway Patrol Marine Operations Division and the Division of Drug and Crime Control were investigating, and autopsies were planned, authorities said.