Eric Wright, 32, and his father-in-law, Nelson, were fishing in the reservoir in the northeast of Livermore in unincorporated Alameda County.
Nelson went to shore, but when he came back the boat was overturned and his son-in-law was missing.
The rescuers started to search the Bethany Reservoir for a missing man about 4 p.m. with the help of divers, search dogs, and helicopters.
Wright is believed to fall down after the boat was capsized, but his fate is still unknown. Water temperature in the reservoir is 49 degrees, thus Wright could have possibly suffered hypothermia if he didn’t manage to get out of water.
The search on Monday brought some results: a man's shoe was found. But it’s still undecided whether the search will be continued on Tuesday if no more traces are found.