Eel River & Plymouth Harbor Watershed Management

The Eel River is approximately 3.9 miles in length from the headwaters at the cranberry bogs east of Long Pond Road to the mouth at Plymouth Harbor. Another branch of the river begins south of Forge Pond and continues north past Clifford Road bridge where it connects to the main branch. The Eel River Watershed is approximately 15 square miles and has been delineated based on groundwater modeling: see the Eel River and Plymouth Harbor Watershed Map (PDF). The Eel River Watershed is a valuable natural resource to the Town of Plymouth not only for its natural resources, but for the aesthetic and recreational opportunities it provides for locals and tourists. This watershed contains approximately 800 acres of open water and is habitat for various fish species and wildlife that create a healthy ecosystem.

The Eel River outlets into Plymouth Harbor which is a valuable resource for the Town. Plymouth Harbor offers aesthetic and recreational opportunities to locals and tourists as well as shellfishing resources. Tourists from all over the world come to visit to explore the history, natural beauty and recreational opportunities Plymouth Harbor has to offer. Famous historical sites are visited daily such as Plymouth Rock and the Mayflower II. Recreational activities including whale-watching, swimming, deep-sea fishing, shellfishing, boating and birding are tourist attractions in the Harbor. Over time, however, Plymouth Harbor has become an impaired waterway listed as 303(d) due to bacterial contamination and nutrient inputs from point and non-point source pollution. The bacterial contamination had contributed to the prohibition of shellfishing for 40 to 50 years in Plymouth Harbor. However, due to the vast work and improvements in water quality approximately 164 acres of shellfishing was opened in 2014 along Long Beach in Plymouth Harbor.

An increase in nitrogen and phosphorus levels can lead to eutrophication which is the over-enrichment of a waterbody with nutrients resulting in excessive plant growth. This excessive plant growth depletes oxygen levels and can cause organisms including fish to perish. Nutrients such as, nitrogen and phosphorus, can enter the river system from various sources including stormwater runoff, fertilization and septic systems.

The Town of Plymouth has an obligation to conduct and implement a Nutrient Management Plan per the Wastewater Treatment Facility (WWTP) Permit. As part of this requirement the Town has been conducting groundwater monitoring, surface water monitoring and biological monitoring in the watershed and within the Eel River.

USGS Real-Time Water Data for Eel River

• Route 3A Gauge
• See information on MEP Linked Watershed Embayment Nitrogen Threshold Analysis