WHATCOM COUNTY, Wash. -- The swimmer who went missing in Lake Whatcom Sunday has been identified as 40-year-old David Johnston of Bellingham.

Authorities continue to monitor the surface of Lake Whatcom for the body of a missing swimmer as they have suspended their search into the 300 ft. depths.

Whatcom County Sheriff Bill Elfo says they’re no longer using volunteer divers since the water in that area has poor visibility.

Elfo says a customs and border protection helicopter is flying over the lake and the Sheriff’s Department is working on borrowing sonar from another county to help find Johnston’s body.

Witnesses say Johnston was swimming back to a boat he was on with other passengers Sunday afternoon when he began to struggle and call for help.

He disappeared underwater and hasn’t been seen since.