Portofino, your post isn't clear. Are you saying that the lots are 300 meters from the beach? If there is that much difference between the lot and the high water line, you will have no trouble.
What Paul is talking about is the law making everything within 60 meters from high water line public property. You can't build on this property unless you have special permission of the government, which normally is only granted to things like tourist projects.
BTW, Paul mentioned paying the Port Comandante to ignore that his garage was too close. Problem with that is that once you start paying, you can never stop. All future comandante can inspect the property, discover that the garage is too close, and order it torn down. Who knows how much each future comandante will need to be paid.