It is already illegal for vessels of any type to discharge raw sewage (unless offshore -ocean- by 3 or more miles) into US waterways. The only parties who get away with dumping raw sewage are municipalities who's waste treatment systems overflow or malfunction (some at an alarmingly regular rate, like every time it rains). What's at stake here are on-board treatment systems. Systems that output treated waste that is many, many times cleaner than what a waste treatment plant discharges. In the words of the Maryland Attorney General's office; on-board treatment systems account for less than .1% of any water quality issues (actually, less than .003% to be exact)! Yet, supporters of NDZ legislation want to criminalize their use.