Even in the confines of Chesapeake Bay, the contribution of human waste from recreational boaters during the summer months is akin to a speck of fly $hit in a mountain of pepper. It's purely political and always has been. Also, you must keep in mind that that waters of Chesapeake and Delaware bays look the same during the dead of winter. Gee, kinda makes you wonder where all that crap is coming from, doesn't it?
The two places that I can truly say have benefited from holding tank laws are Boot Key Harbor in the lower Florida Keys, and Solomons Island Harbor in the lower Patuxent River in Maryland. As Solomons Harbor increased in popularity back in the early 1980s, huge number of sailboats began spending more and more time on the hook there, and nearly all were dumping the tanks at night. By morning the odoriferous waft from the harbor became horrendous. It only took a couple weeks of strict enforcement to eliminate the stench and the harbor returned to it's prior, retched water state within a couple months.
In Marathon's Book Key Harbor, where boats are stacked up like cordwood during the winter months, the pristine, turquoise waters eventually turned slate gray, the turtle grass began to die, lobsters disappeared, fishing went to Hell, and the water smelled just awful. The city took over the marina, two large pumpout boats went into full-time operation, and every boat in the harbor was pumped out on a weekly basis. Enforcement of Y-valve regulations became very strict, and two years later the harbor, while not fully recovered, looks pretty darned good. Underwater visibility at the City Dock was about 6-feet when I left there last March.
Unfortunately, the unabated discharges by outdated municipal wastewater treatment plants, agricultural and industrial discharges and other lesser sources, has severely effected our oceans, and has been for decades. It's the out of sight - out of mind mentality that people in general have, and politicians thrive upon, that created this problem in the first place. It's the "If we can't see it, feel it, or smell it, then it doesn't exist" at least in their minds. Therefore, it's not a problem. Doesn't anyone ever wonder who the idiot was that first dreamed up wastewater treatment plants got into his mind that if we put this stuff in the water it won't hurt anything. I'm not just talking about human waste, I mean anything.
For years Dupont was allowed to dump their chemical wastes offshore and did so just 12 miles out from the mouth of Delaware Bay. At least two major municipalities on the east coast hauled their trash offshore on strings of barges and bulldozed it overboard. Why do you think all that medical waste, syringes, etc..., washed up on the Jersey Shore for decades. At first the feds tried to blame the syringes on junkies tossing their syringes into the rivers, but that was never the case. Junkies don't dispose of syringes - they use them until they're no longer useable.
When will people learn that you cannot continue to dump crap in the water, water that they drink, obtain food from and use recreationally? As far as most people are concerned, they totally believe everything in the world is disposable. Cellular phones, TVs, microwave ovens, cars, trucks, busses, diapers, paper, you name it - even boats. I guess that's why some folks now think it's perfectly acceptable to consume what is referred to as "recycled water." Think about that the next time you turn on the spigot supplying your drinking water.