The bodies of the three persons had burn injuries as in electrocution, said sources in the Tinsukia Civil Hospital where they were brought.
Police sources said the cause of the death would be ascertained only after post mortem was done on the bodies.
Local people said that Naso Chetri (55), his wife Neena (48) and their neighbour Amit Shah (12) had gone to Tingrai river in Tinsukia town when they were electrocuted by a high voltage electric wire that had fallen into the river.