Attapol Suksai, 42, had gone to visit his mother who required some medical help and then headed to meet his wife by taking a boat down the Kaeng Krachan Dam in Phetchburi province.
Strong currents in the dam, however, flipped the boat over and dragged the official under the surface.
Local rescue teams have found the boat but there is still no sign of Attapol, though they believe he may still be alive as he knows about the strong currents and may have taken refuge on a small islet in the reservoir.