Monitoring and Assessment of Coastal (Marine) Waters


Angela Brewer (207) 592-2352; James Stahlnecker (Toxics) (207) 215-6954; Cheyenne Adams (vegetation mapping) 352-8508; Emily Zimmermann (salmon habitat) 446-1003; Eric Rainey (vegetation mapping technician) 332-1309

Maine Estuaries and Coastal Waters page

The Marine Unit monitors and assesses the health of marine waters (estuarine and coastal areas) through the collection of physical, chemical, and biological samples as related to attainment of Maine's water quality standards (38 M.R.S. § 465-B). For further information, see Maine's water classifications and Class SA marine waters.

The Marine Unit provides technical support to the DEP's Maine Pollutant Discharge Elimination System (MEPDES) program for wastewater discharges, as well as for Natural Resources Protection Act (NRPA) permits for coastal development projects. The Marine Unit supports volunteer water quality monitoring and other non-governmental organizations working within Maine's marine waters that engage in protection, maintenance and restoration of water and habitats (see list of partners).

Marine Environmental Monitoring Program (MEMP)

Maine's MEMP was established in 1991 (38 M.R.S. § 410-F) to monitor the "extent and effect of industrial contaminants and pollutants on marine and estuarine ecosystems and to determine compliance with and attainment of water quality standards". Monitoring efforts are focused on ambient water quality, nutrients, and eutrophication indicators, in particular near wastewater discharges.

Eelgrass (Zostera marina) (pdf) is a sensitive indicator of excess nitrogen in coastal waters, and has been the subject of aerial mapping and SCUBA-based monitoring efforts, especially in Casco Bay. These efforts, the values of eelgrass and how it can be protected are outlined in this fact sheet. (pdf)

Reports on Casco Bay eelgrass distribution and percent cover changes:

All mapped seagrass and low tide aerial imagery can be visualized through the Maine GeoLibrary (see “biota” and “imagery”, respectively). As of 2023, the Marine Vegetation Mapping Program (MVMP) (see below) will annually inventory 1/5 of Maine’s seagrass and salt marsh resource.

Marine Vegetation Mapping Program (MVMP)

Maine’s Marine Vegetation Mapping Program (MVMP) was established in 2023 (38 M.R.S. §1805) to survey and delineate the coastwide distribution of seagrass and tidal marsh habitat. Mapping is conducted on a 5-year regional rotation (pdf) starting in the Midcoast Region in 2023 and moving to the Penobscot Bay Region in 2024, the Acadia Region in 2025, the Downeast Region in 2026, the Southern Region in 2027, and then continuing in accordance with the same schedule. The seagrass meadows in Maine are predominantly eelgrass (Zostera marina) and occupy the shallow subtidal and protected lower intertidal locations. Tidal marsh vegetation includes cordgrasses (Spartina alterniflora and S. patens), graminoids, and forbs. The Department of Marine Resources previously mapped coastwide eelgrass distribution and percent cover in 1993-1997 and in 2001-2010. DEP’s Marine Environmental Monitoring Program previously mapped eelgrass distribution in Southern Maine and Casco Bay (see above). The Department of Conservation, Agriculture and Forestry’s Maine Natural Areas Program previously mapped coastwide tidal marsh distribution and community type in 2013-2014. All MVMP seagrass and tidal marsh maps and aerial imagery will be available through the Maine GeoLibrary.

Marine Vegetation Mapping Reports:

Salmon Habitat Monitoring Program

The salmon program monitors water quality and biological communities in Maine's Atlantic salmon rivers and streams in close collaboration with state and federal agencies and non-profit groups, with the goal to restore and enhance the endangered populations of this species.

Surface Water Ambient Toxics (SWAT) Program

Maine's SWAT monitoring program was established in 1993 (34 M.R.S. § 420-B) to determine the nature, scope and severity of toxic contamination in the surface waters and fisheries of the State. The Marine Unit monitors for the presence of toxic contaminants in tissues from softshell clams (Mya arenaria), blue mussels (Mytilus edulis), and lobster (Homarus americanus), among other species.

The Marine Unit has collaborated with other toxics monitoring programs including the former Gulfwatch program, which was administered by the Gulf of Maine Council on the Marine Environment (GOMC), and Mussel Watch, a National Oceanic and Atmospheric Administration (NOAA) program.


Marine water quality standards assessments are documented biennially in Integrated Water Quality Monitoring and Assessment Reports, also known as the 305(b) reports, which include lists of attaining and impaired waterbodies. Assessments are based on data collected by the Marine Unit and external organizations with approved Quality Assurance Project Plans.

The Marine Unit coordinates Maine's portion of the U.S. Environmental Protection Agency's National Coastal Condition Assessment (NCCA) every five years. The NCCA consists of coast-wide sampling of the water column and sediment to characterize the health of the physical, chemical and biological environment. Reports of the status of Maine waters within regional and national contexts are produced by EPA.

Data and Maps

Marine data are housed in DEP's central database, the Environmental and Geographic Analysis Database (EGAD) and in downloadable map projects.

Partnering Organizations

Maine Healthy Beaches

Casco Bay Estuary Partnership

Friends of Casco Bay

Kennebec Estuary Land Trust

Boothbay Region Land Trust

Maine Coastal Observing Alliance