Well, as Danube go first through Slovakia and then Hungary before it gets to Serbia it must be more polluted there. But you know this could also be just different standards in different countries. We are told not to swim in there but it might be just perfectly fine :) We only have a small piece of the river in Slovakia and the current is very strong in these places so it might be good that we don't swim there.

Oh yes, I love Belgrade. People are so nice and there are so many good places to eat. I also loved the night life there :)