Conditionally Approved Shellfish Waters

Maryland participates in the National Shellfish Sanitation Program (NSSP) to protect public health and to assure oysters and clams are harvested from areas that are safe.  The basic concept of the National Shellfish Sanitation Program (NSSP) is to control the safety of shellfish by preventing the harvest of shellstock from polluted harvest areas.  Shellfish include oysters and clams and not crabs, shrimp or lobsters.  MDE classifies all shellfish harvesting areas or growing areas as Approved, Conditionally Approved, or Restricted. 

  • Approved

    Approved means that oysters and clams can be harvested anytime.

  • Conditionally Approved

    Conditionally Approved means that oysters and clams can not be harvested for three days following a rainfall event of one inch or greater over 24 hours.  All other times, they can be harvested.

  • Seasonally Conditionally Approved

    Seasonally Conditionally Approved means that direct harvest is allowed during the months when the area is in an open status (water quality meets the criteria for an approved classification).  The remaining months would mean that the area is restricted or in a closed status.  Relay would still an option when the area is in the closed status.

  • Restricted

    Restricted means no harvesting is permitted.

Conditionally approved harvesting areas generally meet the bacteriological water quality criteria for classification as approved (i.e. open to harvesting at all times) under the NSSP only when a certain definable set of conditions occurs. If these conditions are not met, water quality in the harvest area is generally of lesser quality.  When the conditions causing the water quality to be of lesser quality can be predicted, a management plan can be established which will allow harvesting when the water quality meets the criteria for the approved classification.  Harvest areas regulated under these management plans are placed in the NSSP conditionally approved classification.  In Maryland, the predictable condition is rainfall.

The Maryland Department of the Environment has established a rainfall level greater than or equal to 1 inch in 24 hours as an adverse pollution condition. This determination was based on an investigation and extensive data analysis done in 1987. The results indicated that elevated fecal coliform levels occur following a 1 inch rainfall in some portions of some harvest areas.  The source was determined to be non-point source runoff which could not be traced to any source with public health significance.  Based on intensive data analysis, 3 days were found to be the maximum time necessary for water quality to return to approved area quality.  The water quality in the conditionally managed area was found to meet the approved classification bacteriological standard often within 48 hours and always within 72 hours.  Therefore, placement of the harvest areas in the conditionally approved classification in the closed status for 3 days following the occurrence of the adverse pollution condition was determined to be a sufficient restriction. 

Conditionally approved areas are closed for three days following a rain event of equal to or greater than one inch in 24 hours.  After that, harvesting is permitted unless another rainfall occurs in the area.

Shellfish Fact Sheets

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Contact Information

Please direct questions or comments about Maryland's Shellfish Monitoring Program at (410) 537-3818.


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