>>598
Just finding out who's responsible won't do any good since only those who get caught learn lessons from that; not to mention that'd be extremely difficult.
My idea is putting up a poster with something along the lines of "CLEAN BEACH OF NICE VISITORS" which will be having good influence on people's behavior in the long run. Classic reverse psychology.
Secondly, keep beach clean by local officials everyday, then they won't even dare to make a mess there; which is another example of how people's minds work.