The Massachusetts Department of Environmental Protection’s GIS map is a resource that displays information about all Combined Sewer Overflows (CSOs) throughout the Commonwealth. Each CSO is marked with a link to a pop-up window that displays a wealth information, including: the National Pollutant Discharge Elimination System (NPDES) permit ID, the system that it belongs to (Cambridge, Somerville, or the MWRA), the CSO ID, the location, and a link to the permit which allows for the legal discharge of sewage contaminated water into the receiving water body.