Water Quality Management

How is water quality managed in the State of Maine? In the fields below, the MSLN hopes to provide some general information on policy regarding water quality, shellfish area closures, and different state and national programs. This structure is also described on the Department of Marine Resource Website, here.

Water Quality Management in Maine

National Shellfish Sanitation Program

The National Shellfish and Sanitation Program (NSSP) was developed at the federal level from the U.S. Food and Drug Administration, and created a series of nationwide laws which protect consumers from any shellfish contaminated with pollution. To read the most recent edition of the NSSP, click here.

Department of Marine Resources

The Maine Department of Marine Resources (DMR) oversees the application of the NSSP within the context of Maine’s shellfishery. Specifically, the DMR monitors for biotoxins such as “red tide”, and water quality. The DMR assigns stations within mudflats and samples water at each station on an annual basis. Each water sample is tested for fecal coliform bacteria, a variety of bacteria that come from fecal pollution in the water. These scores are then processed within a p90 statistical analysis. This analysis takes 90% of 30 individual tests and assigns a final score. 30 individual tests at a station usually means about 5 years of testing. Depending on the score, the DMR will close, open, or conditionally open clam flat areas. To read more about a p90 score and other types of water quality related information, please visit our water quality information guide.

Figure of Water Quality Management (G. Hillyer 2019 Thesis)

Types of CLosures

As stated in the section above, there are multiple types of closures depending on the final score from the p90 of a station. Below, we describe each of these closures. To find a closure map, ask questions about the coloration or image, or for further details about the types of closure, please visit the DMR public health page, here.


A Prohibited closure means that the final p90 score is greater than 163 CFU/100 mL. This number is derived from the NSSP. Prohibited areas are not allowed to be fished in any capacity until the p90 drops lower than 163 CFU/100mL. There are also prohibited areas that are policy closures due to the presence of point source pollution, for example a dilution area around a marina or active overboard discharges.


Conditional approved or conditionally restricted areas are areas that can be temporarily closed based on environmental conditions that can be managed. For example, in Maine, conditional closures can be managed based on rainfall, season, the presence of a marina, astronomical high tides, or river flow. Runoff, in this instance, means when rainwater flows out to the river estuary and mudflats, carrying pollution. In certain areas across the coast, clam-meat studies were done in order to change the timing of closures. For example, in the Medomak River, conditionally approved areas are closed when rainfall meets or exceeds 1″ within a 24-hour period, and are closed for 9 days.

Flood Closure

Flood closures close when rainfall meets or exceeds 2″ (5cm) in a 24-hour period due to the potential for fecal coliform pollution caused by runoff. This is a policy in Maine, so it happens throughout the state. Reopening after a flood closure is based on sampling by the DMR.


These are areas that are greater than 31 and less than 164 CFU / 100mL, but you are able to harvest with a special DMR permit for depuration digging.