The Multnomah County Sheriff’s Office Dive Team is expected to begin recovery efforts this morning for missing swimmer on the Columbia River. A man in his 50s was on Ackerman Island Wednesday night when his boat became unanchored from the shore just before 9 p.m., according to the Multnomah County Sheriff’s Office. The man swam after the boat but drifted into the river channel and disappeared from view, the sheriff’s office said. Boats from the Multnomah County Sheriff’s Office and the Vancouver, Gresham and Portland fire departments responded and assisted in the search Wednesday night along with a US Coast Guard helicopter. Crews used sonar, thermal imaging and drag bars, but suspended the search at about 11 p.m.