Saturday 14 July, called out at 1400 hours ATL male adult drowing victim in Dry Lake near Manson, WA. Hasty search via mask & snorkle after boats and helicopter UTL. Side scan sonar unable to pick up victim, heavy milfoil infestation blocked anything beyond/among vegetation. Dove on 15 July for 38 minutes max depth of 20` in search pattern along shoreline with V, MB, MH, B. Milfoil so thick vis was 0-3 feet max and significant tangling hazards. UTL. Subject floated and recovered following day.