The incident happened in the town of Akyazi, in Sakarya province, 100km (62 miles) east of Istanbul.
The park manager and his son dived in to help the three children. The five, believed to be all Turkish, were taken to hospital but could not be saved.
It was unclear how the pool had become electrified.
Rescuers and park personnel flushed the pool's water away as others turned off electricity in the facility.
One other person was injured in the incident and taken to hospital.
An investigation has already begun.
The Hurriyet newspaper named the park manager as Mehmet Kaya, 58, and his son as Kadir Kaya, 30.
The children were aged 12, 15 and 17, Turkish media said.
Three children and two adults who tried to rescue them have been electrocuted in a water park in north-western Turkey, local media say.