No Discharge Zones (NDZs) directly address the human health and environmental concerns created by the release of boat sewage into coastal waters. Sewage wastes discharged from boats can contain microorganisms (bacteria, viruses, and protozoans), nutrients, and chemical products—all of which can have harmful effects upon aquatic life and water quality.

Even small amounts of microorganisms from sewage wastes can introduce diseases like hepatitis to people in contact with the water. Bacteria can contaminate shellfish and make them unsuitable for human consumption. Many marine sanitation devices (MSDs) discharge "treated" waste with bacteria counts up to 70 times higher than that allowable under state law for shellfishing or swimming waters. In addition, there is no annual inspection program to ensure that installed MSDs are operating as advertised. Without routine maintenance, it is entirely possible that an MSD is not providing the level of treatment that a boat owner thinks it is providing. Prohibiting all boat sewage discharges in NDZs ensures that poorly maintained MSDs do not degrade water quality and helps reduce the risk of human illness from inadequately treated sewage.

Excessive nitrogen can be a problem in poorly flushed embayments because it stimulates harmful algal growth and contributes to reductions in dissolved oxygen. Both of these conditions can decrease the survivorship and reproductive potential of marine life. None of the MSDs available today are designed to reduce the nitrogen concentration in "treated" wastes. Prohibiting MSD discharges in NDZs helps to reduce nitrogen inputs to sensitive waters.

To help reduce odor, some boaters add chemicals to their heads (marine toilets) and MSDs, which can be toxic to marine and estuarine life. Using non-toxic deodorizers and pumping out wastes at designated facilities helps to keep these contaminants out of coastal systems.

Complying with vessel sewage discharge regulations and using pumpout facilities are necessary steps toward protecting public health, water quality, and the marine environment.