As of 2014, all of Massachusetts waters have been designated as “no discharge” for vessel sewage (see Massachusetts NDZ map, PDF 1.2 MB).
It is a violation of federal law to discharge treated or untreated boat sewage within Massachusetts waters. In January 2009, legislation was signed that gives the director of the Massachusetts Environmental Police, and all that serve under him, the ability to issue an administrative penalty not to exceed $2,000 per infraction for violations of NDZ regulations. This enforcement authority applies to environmental police officers, harbormasters, fish and game wardens, and police officers assigned to patrol the waters of the Commonwealth. Specifically, the law states that no person shall discharge any sewage, whether treated or not, from a marine sanitation device into any waters of the Commonwealth designated by the Secretary of Energy and Environmental Affairs as an NDZ. As of 2014, all of Massachusetts waters are an NDZ, so it is illegal to discharge sewage, whether it is treated or not, from any recreational, commercial, or residential vessel. (For more information on who can enforce NDZs, see MGL 90B Section 12.)
For more information on penalties, see MGL 90B Section 5C.