“My and my neighbor’s property lines run across the same pond and back to land on the other side, splitting the pond in 3 sections. Questions exist as to if property lines exist within water, and thus required to stay within property lines, or does entire pond become available for full use of all 3 owners?”
The first thing you would need to do to answer that question is look at the actual deeds. There may be provision in one or more of them regarding the use of the pond, and that would answer your question directly.
Even if not, however, if the owners have in the past made use of the entire pond, they may have developed rights in the way of a prescriptive easement. This would be the case where continuous, open use was made for the appropriate period of time (which varies by state), and without permission having been given.
If you are looking to make a specific use, or deny a specific use of the pond, you would do well to first review the history of the property before taking a legal position. And in the interest of neighborliness, try to work out an agreement before taking any legal action.