The boy and his father were sledding along the Mustionjoki River in Karjaa, about 75 kilometres west of Helsinki, when the boy's sled slid out onto the ice and into an a patch of open water.
The father followed into the water and tried to save his son, but strong currents had already swept the boy under the ice and threatened to do the same to him. Hearing his cries for help, a passerby used her coat as a rope to keep the man afloat until emergency crew rescuers arrived.
Divers found the 4 year-old boy trapped under the ice 70 metres from shore and began resuscitation efforts immediately. He was sped to Helsinki's Children's Hospital, from where he was released on Tuesday and returned home in good health.