The Massachusetts Department of Environmental Protection (DEP) has promulgated new regulations intended to reduce nitrogen loading from septic systems in sensitive coastal estuaries and embayments in the Commonwealth, with an initial focus on Cape Cod. These regulations took effect as of July 7, 2023, and will have a significant impact on the owners of thousands of properties with septic systems in areas where the new regulations apply. They amend DEP’s Title 5 regulations, 310 CMR 15.000 et seq., which regulate the construction and maintenance of on-site septic systems. They also establish a new regulatory program for municipal watershed permits at 314 CMR 21.00 et seq.