text: #1.When a body floats it displaces fluid (water here) equal in weight to its own weight. \n\n#2.Buoyancy is equal to weight of the fluid displaced\n\nso that we can say for a floating body: \nbuoyancy = weight of the fluid displaced = weight floating body\n\n#3.Sea water density is more  than that of  fresh water, \n\nso a lesser amount of sea water provides the required buoyancy to enable the swimmer float, and less sea water needs to be displaced. \n\nThis makes the job of swimmer easier.\n\n[BTW: A boiled egg floats easily in salty water for the same reason]