Stopping pollution is easier said than done. Keep in mind that every time a newborn baby enters this part of the world, that baby poops in Chesapeake Bay. It does this many, many times during it's lifetime, and it produces offspring that compound the problem. Now, that person, whom will likely live more than 70 years, requires a significant volume of food in order to survive. The person will likely consume a huge quantity of beef, pork, poultry, vegetables, fruits, etc..., animals that produce lots of nutrients that will wash into the bay's tributaries, and eventually end up in the bay.
This process, reproduction, which is part of human behavior, is not something that will go away. It will continue throughout time, and you must take into consideration that human populations are still increasing worldwide - not just in the Mid-Atlantic region. As those populations grow, each and every person born poops into the bay. This is not going to stop - ever. We keep building more and more homes, and more and more sewage treatment plants to cope with the population expansion. Those treatment plants cannot possibly keep up with the population increases, thus the waters of the bay and its tributaries will continue to worsen. This isn't rocket science - it's just common sense.
Many years ago I published an article about the bay's water quality and why it would never get better. I cited as an example the Susquehanna River, which at the time was listed as the most polluted river in the nation. When the article was published there was approximately 130 sewage treatment plants on the Susquehanna River between NY and the head of Chesapeake Bay. The last line in the article stated "If the good people of Harrisburg, PA do not flush their toilets, Havre de Grace, MD would not have any drinking water." The editor didn't like the line, but he agreed that this was indeed the case. Someone wrote a letter to the editor saying this just revealed how well those sewage treatment plants work. In reality, the plants, nearly all of them, were running at more than 200 percent over their rated capacity. The treatment at that time was huge doses of chlorine to kill the bacteria prior to discharging the water into the river.
A few years ago, when Maryland was experiencing a horrendous drought, the city of Frederick, MD considered piping its waste water into the city reservoir, which at the time was nearly bone dry. An early season hurricane solved their problem, but that water was nothing but a muddy torrent that flowed in from the creeks feeding the lake.