Puzzle of Keep the beaches clean

At Monemvasia we see a sign that explicitly asks that the beaches be kept clean, a school project that will hopefully catch on. Most of the beaches that we have seen so far have been reasonably clean, but there is still too much junk.

---

When you don't see the puzzle, please check whether your device can handle html5 or java. Read here why the puzzles look different and which problems there can be