Classification of Shellfish Growing Areas

National Shellfish Sanitation Requirements

DSS classifies shellfish waters using the requirements and standards of the National Shellfish Sanitation Program (NSSP). Virginia’s shellfish program must conform to the NSSP in order for its shellfish industry to engage in interstate commerce. Click here for detailed NSSP requirement information.


Bivalve molluscan shellfish (oysters, clams, mussels, etc.) feed by pumping large amounts of water through their gills and filtering out their microscopic-sized food particles. Along with these small particles, they also filter out bacteria and viruses from the overlying water. Since these shellfish may be eaten raw, which includes their intestinal tract, care has to be taken to ensure that shellfish harvested for direct marketing are taken from very clean water. Waters approved for the direct harvest of shellfish therefore must be much cleaner than waters approved for swimming, fishing, etc.

Shoreline Survey Program

The first step the Division takes in determining the proper classification of shellfish waters is to conduct a shoreline survey. In order to correctly classify shellfish waters as to their suitability for the direct marketing of shellfish, the watershed must be examined for the presence of actual and potential sources of pollution. This survey involves visiting all properties on the drainage basin of the area that are deemed capable of impacting shellfish waters. The primary concern is the presence of fresh fecal matter. All onsite sewage facilities are investigated to see if they are functioning properly, and all potential sources of other pollution including animal waste, toxic substances, industrial discharges, marinas, wastewater treatment facilities, etc. are inspected. Sewered areas are noted, but not investigated. The field data and other pertinent information is compiled into a report accompanied by a map of the area. The map shows areas where property inspections occurred as well as those properties which had an actual or potential pollution source found on site. These are indicated on the map with symbols that represent the type of pollution found. The final report and map is sent to the locality and the state agencies responsible for the various types of problems found. DSS investigates an average of 13,000 properties per year, and conducts new shoreline surveys every 8 to 9 years.

Seawater Sampling Program

The second type of information used in classifying shellfish growing waters is the concentration of fecal coliform bacteria present in the water. The Division maintains boats at each of its field offices and collects samples minimally six times per year at designated stations throughout the shellfish growing waters in tidal rivers, Chesapeake Bay and Seaside Eastern Shore. Sampling is scheduled a month in advance so that the samples will be collected randomly with respect to the weather, i.e.under all weather conditions except those that pose a hazard to the crew. The samples are analyzed in the Division’s own laboratories for the concentration of fecal coliforms present in the growing water samples. DSS collects and analyzes over 24,000 seawater samples per year. In addition, such hydrographic information as temperature, salinity, turbidity, stage of tide and rainfall data for the sampling area are measured or otherwise obtained.

Central Office Classification

Once the shoreline survey results have been examined to determine the locations and effects of the actual and potential pollution sources, the seawater sampling data is used to make the final classification determination. These formal evaluations are made annually, though the microbiological data analyzed and entered at the field offices is computer-analyzed monthly to determine whether valuable shellfish grounds can be opened. In such cases a new formal evaluation is conducted in the central office, and if possible, the portions of the growing area that have improved water quality are opened.

Some portions of shellfish growing areas are either permanently or seasonally closed to direct shellfish harvesting due to the presence of either marinas, wastewater treatment facility discharges or other seasonal activities affecting water quality. In the case of marinas and wastewater treatment facility discharges, DSS uses a computer model to determine the size and shape of the closure area based on the potential fecal input, e.g., number of boats in a marina or the number of gallons of sewage permitted for the treatment facility. The Division is careful to ensure that a sufficient area is closed to protect public health under even high pollution events without condemning excessive waters.

Fecal coliform organisms are used as an indicator of fecal pollution from warm blooded animals and the national standard is a geometric mean of 30 samples not to exceed 14 fecal coliforms per 100 ml of seawater. A second part of this standard addresses the variability of the data, and requires that the estimated ninetieth percentile not exceed 31.

In 2007, the Division changed its testing methodology from a multiple tube fermentation method to a membrane filtration method. This method yields lower variability in fecal values because it directly counts the fecal bacteria colonies. This lower variability will reduce the 90th percentile to 31 when thirty samples for a given station have been analyzed using the new method.

To put the shellfish standard for fecal coliforms into perspective, note that an often used upper limit for swimming is a geometric mean of 200, thus the shellfish standard is at least 14 times more restrictive than the swimming standard.

If you are an oyster gardener or a clam aquaculturist

Many people are becoming interested in growing shellfish for fun, as a method to help filter water and clean up the Chesapeake Bay, to have a few to eat, or for profit. DEQ’s Coastal Zone Management Program has a web site with helpful information – go to their Virginia Oyster Gardening Guide web site for helpful information. If you are considering culturing shellfish for either personal use or sale, it is most important to be sure that the water is sufficiently clean. We will need to conduct a special assessment of the water quality in the vicinity of the area in which you plan to grow shellfish for sale.

Whether for commercial aquaculture or personal use, all aquaculture activities on state owned bottom or in floats, require either a bottom lease or permit issued by the Virginia Marine Resources Commission (VMRC). Contact your local VMRC office or their main office in Newport News at 757-247-2200 for more information.

If you do plan to sell the shellfish directly to market (for example to a restaurant), then you must first be certified by our Division. Contact the DSS Field Office closest to your area, and we will be glad to help.