The two were using their long-tail boats to catch fish in the reservoir when the accident occurred about three kilometres away from the pier.
The two boats sank and Somchai Chana, 49, went missing while Banphot Sathit, 65, managed to swim ashore.
Police said the engine of Somchai’s boat cut out and Banphot’s vessel, which was following, crashed into it. They said Banphot could not stop his boat in time.