Assess the level of pollution
Firstly, you will have to assess the overall level of the beach pollution. It may not be out of control yet and you can do small things to improve the situation. Therefore, go to the beach and note what you feel is wrong in terms of beach pollution. You can then prepare a document and post it to the concerned government department.
Spreading awareness amongst people was not the easiest of tasks a few decades ago. However, things have changed to a great extent and you can share your message with the entire world through the Internet. Educate the people around you, using the social networking websites. You can make a huge contribution by doing this.
Pick up trash from the shores
Another thing you can do is cleaning up the trash from the shores. You can involve your friends, colleagues and other concerned people. Even if you are alone, start doing so on your own and there will be a lot of people, who will follow your example.
Help the authorities
There are some spots on every beach where the effect of low water is most prominent. Throwing garbage at these places will cause greater pollution. If this hasn't been done yet, help the authorities make a note of that. Those specific spots should be banned for public.
Also campaign for starting a fine system for the violators.