Expedition swimmer
From Openwaterpedia
noun - An expedition swimmers is an individual who swims in natural or man-made open bodies of water including oceans, lakes, rivers, bays and reservoirs, together with teammates or swim buddies, usually as part of a guided tour with or without escorts.
Usage
The expedition swimmers enjoyed their holiday swim in Baja California where they saw many dolphin.
Synonyms
wild swimmer, open water swimmer, free swimmer, sea trekker, swim trekker
Sea expedition led by Masayuki Moriya of Ocean Navi on the Izu Peninsula on Honshu in Japan