If the waterway is considered navigatible it is public. If not, the property under it belongs to the surounding land owner. This is only a general rule. It is best to contact the local DNR officer if you are unsure. Do not ask the local law inforcement agency as they are often unfarmilar with game laws. Trust me on that. Talking from experiance. I had to give 4 local cops and 2 county sheriffs a lesson inwaterfowling law. They still didn't want to believe me until the local DNR officer showed up after I called him.