As many people have pointed out, the answer to whether you can publicly access water depends on the state. Here in New Hampshire, any pond (natural or manmade) is publicly accessible if it is 10 acres or larger. This size also seems to be a pretty common standard, at least in the New England states. In your case, since the pond is only 8 acres, I would say that you have rights to the section that is on your property. Like a lot of people have said, though, is the other owner really going to have a problem if you pull a bass out on his portion? If you are really worried, or interested, then I would do a quick Google search on Louisiana water access laws. Louisiana is actually a special case, too, because your legal system is partially based on the old French civil law. I don't know what effect this will have.