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MassGIS Data: MassDEP Mouth of River Lines

March 2005 (Digital version January 2023)

This layer contains the Mouth of River (MOR) lines for Massachusetts coastal rivers originally published by the Massachusetts Department of Environmental Protection (MassDEP) on March 1, 2005, as PDF maps.

Table of Contents



The PDF maps identify the mouth of the river for coastal rivers in order to provide a clear, consistent, and predictable means of locating all river mouths in the Commonwealth. They are the final MOR maps for each community and represent the culmination of a year's effort that included distribution of draft maps for public comment, receipt and review of over 100 written comments, and field surveys for many of the more difficult mouth of river lines. Each Massachusetts coastal community received a set of maps corresponding to the rivers in their community.

The MOR map lines are intended to

  • identify where a river ends pursuant to 310 CMR 10.58(2)(c). As provided in 310 CMR 10.58(2)(c) "When a river flows into coastal waters or an embayment, the river shall end at the mouth of coastal river line as delineated on the current mouth of coastal river map series maintained by the Department." 
  • represent the limit of Riverfront Area jurisdiction under the Wetlands Protection Act. Land upstream of the MOR line includes Riverfront Areas subject to the protections afforded by the Wetlands regulations; any land seaward of the MOR line is not subject to jurisdiction as a Riverfront Area but remains subject to other inland and coastal provisions of the Wetlands Protection Act.

By adopting a uniform approach to mapping river mouths, this data should reduce the need for individual MOR delineations and in turn provide a predictable means for project review for landowners, conservation commissions and MassDEP.


The polyline features in this layer are based on field observations conducted by MassDEP Wetlands Program staff and were originally published on March 1, 2005 on MassDEP's website as Portable Document Format (PDF) files. Designations of perennial streams on the United States Geological Survey quadrangle maps served as the basis for the initial identification of all rivers in Massachusetts. The field observations were transcribed onto USGS Quadrangle Maps. The corresponding points of land on the opposite banks identified in the field where the river flows into coastal waters or an embayment were digitized, then a polyline was drawn between the two corresponding points. The polylines were drawn based on MassGIS 2001 & 2003 Aerial Imagery, which was the most recent available aerial imagery at the time.


The DEP_MOR_ARC attribute table includes the following fields:

Field   Type   Description
RIVNAME   Text   River name
TOWN   Text   City/town in which the river is located
MOR_ID   Text   Unique MOR Identifier

Criteria used to determine the Mouth of River:

A - End of parallel banks: point at which bank to bank river mouth line loses approximate "perpendicular" nature
B - Visual characteristics of apparent sub-marine channel on orthophoto maps
C - Identifiable landward edge of bank interface with coastal beach or vegetated dune
D - Seaward edge of salt marsh
E - Inland of named features shown on the most current USGS map including coves, harbors, bays, embayments, salt ponds (including those with CZM salt pond designation), sounds, as well as "guts" and "straights" that connect ocean feature to ocean feature
F - Downstream side of control structure designed as barrier to coastal flooding (e.g. dike, tide gate, or solid fill causeway).

LENGTH   Double   Length of feature in meters

Terms of Use

These maps are required to be used pursuant to 310 CMR 10.58(2)(c) to identify the location of the Mouth-of-River. If a mouth of coastal river line is not delineated on the current map series, the issuing authority shall determine the mouth of coastal river line in accordance with the Department’s most current Mouth of Coastal River Policy. A mouth of coastal river line shown on the Department’s mouth of coastal river map series is not evidence that a stream is perennial; such a determination shall only be made pursuant to 310 CMR 10.58(2)(a)1.


The MassDEP Wetlands Program maintains the data. Contact: DEP.Wetlands@mass.gov

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