> the difference in density between seawater and fresh water is about 3%, and it's noticeably easier to swim in the sea This really messed with my head when I

> the difference in density between seawater and fresh water is about 3%, and it's noticeably easier to swim in the sea This really messed with my head when I swam in Lake Constance last year. I was so used to swimming in salt water than the different buoyancy in fresh water completely threw me off for a couple of minutes.