永 'forever' was originally itself a picture of a person swimming along a long river branch — endlessness drawn as water that keeps going. When 永 settled into meaning 'eternal', the water radical was added back to restore the swimmer: 泳.
游泳 pairs two swimming characters into the standard word. Winter swimmers (冬泳爱好者) who break ice in Harbin to swim at -20°C are a national photo-op every January — endurance as performance art.
永 was a swimmer all along — add water 氵 and the stroke goes on FOREVER.
泳道 'swim lane' borrowed itself into office software: kanban 'swimlanes' are 泳道图 in Chinese project management.