Question

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

Answer 1

As you know, salts are dissolved in sea water. This makes it denser than river water. So, you would be able to float easier in sea water than river water as objects float on denser water.

Answer 2

as we know that sea water is salty ie. it has salt dissolved in it. river water isn't salty. therefore, sea water has higher upthrust force. since it has higher upthrust force, body comes to the surface of water. so, it becomes easy to swim in sea water than in river water.

hope it helps..