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Blue Hill Bay Watershed Monitoring Project

Located in one of Maine's large coastal sub-basins, the Blue Hill Bay/Mt. Desert Frontal Drainage is a watershed that encompasses approximately 407 square miles of land in Hancock county all of which drains into Greater Blue Hill Bay. The watershed is characterized by multiple land uses including commercial centers of Ellsworth, residential areas, open pasture and row crop agriculture as well as protected acreage (Acadia National Park and local conservation areas). There are also multiple municipal waste water treatment plants and landfills, unmonitored residential septic systems, grand-fathered overboard discharges, marinas and boatyards within the boundaries of the watershed. As population growth and development pressure continues to strain area resources, there is a fundamental need to understand the health and capacity of the watershed.

The Blue Hill Bay Monitoring Project was created in 2004 in order to generate baseline data for these previously unstudied areas in the hopes that the data will be used as a guide for future monitoring and ecosystem-based resource management in the region. The data gathered is used to verify water quality standards, identify sources of pollution, and increase awareness of the need for sustainable watershed management. This project was initiated with the help of the Maine Department of Environmental Protection, the Town of Blue Hill, environmental organizations, and community volunteers to establish a long term scientific assessment of water quality in and around Blue Hill Bay.

Between April and October, 44 freshwater and marine sites are monitored weekly and offshore sites are monitored bi-weekly. Sites were selected to provide a representative sample of watershed conditions, include various land use types, and monitor potential point sources of pollution such as the municipal landfill.  

All sites are monitored with a multi-parameter probe for dissolved oxygen, temperature, salinity, conductivity, turbidity and chlorophyll a. In addition to these parameters MERI staff also collect samples for laboratory analysis of E. coli and Enterococcus bacteria levels along with nitrate and phosphate concentrations.

Analysis of nutrients (nitrate and phosphate) and bacteria is conducted in the Institute’s Marine Laboratory, located at the Center for Marine Studies. Nitrate and phosphate analysis are conducted on a Hach DR 4000 spectrophotometer following EPA approved techniques. Freshwater samples are analyzed for Enterococcus bacteria following IDEXX  Enterolert procedures.

Dissolved Oxygen Levels and Nutrient Loading

While many sites within the watershed remain in relatively good health, a few locations continue to exhibit signs of distress from low dissolved oxygen.  One site at the upper portion of Carleton Stream which flows between Third and Fourth Ponds is heavily inhabited by beavers resulting in dams that clog this waterway. A large dam was removed after a request from the Town, resulting in better flow between the ponds. Although still low, the dam removal improved oxygen levels at this site.

Excessive nutrients and elevated bacteria continue to be detected in our newest area of concern, Little Peters Brook. This site was extensively monitored during the 2008 season but the source of its pollution remains unknown. Monitoring Little Peters Brook highlights the challenge of locating non-point and point source pollution in the watershed.   

Monitoring Mussel Aquaculture in Blue Hill Bay

The State of Maine currently leases approximately 700 acres to shellfish farms along the Maine coast. Of these, 147 acres (21%) are leased to farms located in Blue Hill Bay, and there is public concern about the rapidly increasing number of mussel aquaculture farms in the Bay. Anoxic conditions (dead zones) can occur under mussel farms due to a build up of organic material and dropped shell.

The lack of available information on the impacts of mussel aquaculture on the health of the bay prompted MERI to include these sites in its offshore monitoring program. MERI researchers began sampling nutrients at a depth of 5 meters in addition to the sample normally obtained at 0.5 meters at all offshore sites in 2007. MERI continues to collect data on water quality around mussel farm lease sites in Blue Hill Bay. This data is not being currently collected by the State and may prove important to the ongoing public debate over mussel aquaculture expansion in Blue Hill Bay.

Data Sharing
The Institute shares its water quality data with other scientists, monitoring groups, resource managers, and the public through the PEARL database, an interactive site which is searchable by watershed, town or county. Found at the University of Maine website, the PEARL database has access to all the data generated by the Blue Hill Bay Monitoring Project since the program’s inception in 2004. You can access the site by clicking the link here:


Blue Hill Bay is prime real estate for harbor seals, especially during spring and summer when pups are born on its rocky ledges and islands.

Click here to learn more about Maine harbor seals and the Institute’s Pinniped Monitoring Program


Center for Environmental Studies

55 Main Street
PO Box 1652
Blue Hill, ME 04614
Tel: 207-374-2135
Fax: 207-374-2931
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