US and Canadian marine sanitation law prohibits the discharge ("includes, but is not limited to, any spilling, leaking, pouring, pumping, emitting, emptying, or dumping.") of "sewage," defined by the CFR as "human body wastes and the wastes from toilets and other receptacles intended to receive or retain body waste." Iow, both urine and solid waste.

There actually is a reasonable argument against dumping urine...it's has a fairly high BOD--not enough to matter when it's just one "flush" at a time, but even a couple of gallons at a time (as in, for instance, an AirHead urine jug?) in a cove or anchorage that doesn't get much flushing from nature can have a negative impact.

Btw, not only are all the Great Lakes NDZs, but NY state law prohibits even having any overboard discharge plumbing connected on any vessel on Lake Champlain...and that includes transient vessels, even though Champlain is a navigable INTERstate waterway...and navigable interstate waters are under federal jurisdiction. Federal law (33 CFR 159.7) spells out in detail the acceptable methods of securing a system...they do NOT include the need to disconnect ANY plumbing. However, state law in NY ONLY accepts disconnected plumbing on ALL vessels on Lake Champlain, even on transient vessels. Can they legally do that? Anything is enforceable till it's successfully challenged in court, and so far, there hasn't been a transient vessel owner who's been willing to risk being given the first opportunity to become a test case...they'd all rather comply--a textbook example of the same kind of effective bullying the mob has used for years to extort "protection" money from small businesses.