The RCMP say 36-year-old Brett Smith of Prince George was staying at Takysie Lake Resort, about 50 kilometres south of the community of Burns Lake.
Smith's family contacted police last Thursday to report him missing, saying they were concerned because they hadn't heard from him in two days.
The owners of the resort found Smith's boat, abandoned with his belongings still inside, on the shore of Takysie .
The RCMP and local search-and-rescue personnel headed to the lake, but after four days they have been unable to find the man.
Officials are currently using a sonar unit, police dogs and a helicopter in their search, but they say Smith has likely drowned in the lake.