Question

Which water has lesser density river water or sea water

Answer 1

river water has more density because it does not have any substance mixed in it but sea water is more denser because it has salt dissolved in it.

I hope u understood

Answer 2

river water has less density.this is because it pure and doesn't has many compounds in it so there is less mass in its volume
sea water is dense because it is mixed with many compounds like nacl mgcl2 etc. Sea water has therefore much mass per unit volume leading to higher density
you can float on sea water of dead sea!
good luck