Why is it easier to swim in sea water than in river water?

(N/A) It is easier to swim in sea water than in river water because sea water contains dissolved salts,which increases the density of the water. According to Archimedes' principle,the upthrust (buoyant force) acting on an object is given by $F = V \rho g$,where $V$ is the volume of the displaced fluid,$\rho$ is the density of the fluid,and $g$ is the acceleration due to gravity. Since the density of sea water is higher than that of river water,the upthrust exerted by sea water is greater. This increased buoyant force helps the body float more easily,requiring less effort to stay afloat.