Molluscan shellfish such as clams, oysters, and mussels feed by filtering large volumes of seawater. Along with food particles they can also absorb bacteria, viruses, and other contaminants that are present. If contaminant levels are high enough, shellfish harvested from these areas can make people sick.
Staff working in the Growing Area Program continually analyze marine growing areas to make sure shellfish there are safe to eat. This work involves:
- Evaluating shellfish growing areas.
- Classifying shellfish growing areas based on the results of the evaluation.
- Monitoring shellfish growing areas for changes in water quality.
We have created an interactive map based viewer for commercial shellfish harvesters and others to view data related to the classification of commercial shellfish growing areas. The map shows growing area classifications, marine water quality, commercial harvest site locations, and other data. Create maps, view data, and export data to create charts, graphs and tables using the viewer. The viewer is updated regularly.
The evaluation process is called a "sanitary survey" and involves:
- A shoreline survey, which identifies pollution sources that may impact water quality. We evaluate sewage treatment plants, onsite sewage systems, animal farms, drainage ways, and wildlife.
- Marine water sampling to determine fecal coliform bacteria levels in the marine water.
- Analysis of how weather conditions, tides, currents, and other factors may affect the distribution of any pollutants in the area.
Growing area classifications are assigned based on the results of the sanitary survey. The classification determines whether or not shellfish in the area can be harvested for human consumption. Commercial harvest is not allowed in areas that are not classified.
Commercial growing areas and recreational growing areas carry slightly different classification names.
Commercial Growing Area Classifications
Approved – When the sanitary survey shows that the area is not subject to contamination that presents an actual or potential public health hazard. An Approved classification authorizes commercial shellfish harvest for direct marketing.
Conditionally Approved – When it meets Approved criteria some of the time, but does not during predictable periods. During these periods the area is closed. The length of closure is predetermined for each Conditionally Approved area, and is based on water sample data that show the amount of time it takes for water quality to recover and again meet Approved criteria. Once that time period has elapsed, the area is reopened. Here are two examples of when a Conditionally Approved area would be closed to harvest:
- During dry weather an area may meet Approved water quality standards, but after a certain amount of rain falls (termed a "rainfall event") the water quality declines. The area is temporarily closed to harvest after a rainfall event.
- Some bays are rarely used by boaters in the winter but experience high boater use in the summer. Under these circumstances the bay is open for harvest during the winter and closed during the boating season.
Restricted – Water quality does not meet standards for an Approved classification, but the sanitary survey indicates a limited degree of pollution from non-human sources. Shellfish harvested from Restricted growing areas cannot be marketed directly. They must be relayed (transplanted) to Approved growing areas for a specified amount of time, allowing shellfish to naturally cleanse themselves of contaminants before they are harvested for market.
Prohibited – When the sanitary survey indicates that fecal material, pathogenic microorganisms, or poisonous or harmful substances may be present in concentrations that pose a health risk to shellfish consumers. Growing areas adjacent to sewage treatment plant outfalls, marinas, and other persistent or unpredictable pollution sources are classified as Prohibited. Commercial shellfish harvests are not allowed from Prohibited areas.
Recreational Beach Classifications
Open – The beach meets health standards and the area is safe to harvest.
Conditionally Open – The beach meets health standards and the area is safe to harvest; however, certain conditions can cause an unsafe harvest and the beach will be closed. The beach may also contain multiple classifications. Excessive rainfall, boating, and certain seasons may result in permanent or temporary beach closures.
Emergency Closure – The beach is temporarily closed. Shellfish are not safe to eat. (See Emergency closures below.)
Closed – The beach does not meet health standards and is closed. Shellfish are not safe to eat.
Unclassified – Health standards have not been evaluated for this beach. Shellfish harvesting is not recommended.
Open classifications don't always mean you can harvest. The Department of Fish and Wildlife sets limits and harvest seasons to prevent overharvesting. Check Fish and Wildlife's website to make sure you can legally harvest there.
Once classified, all active growing areas are regularly monitored. Marine water samples are collected throughout the year. Shoreline surveys are conducted less frequently, but each year many shellfish growing areas are surveyed. During those surveys, all potential pollution sources that may impact water quality are evaluated. The purpose of continued water sampling and shoreline surveys is to make sure that growing areas continue to meet the standards associated with their classification, to modify classifications when needed, and to notify the responsible agencies about identified and potential pollution sources.
Occasionally an event occurs that degrades water quality. Floods, sewage spills, and other pollution events can create conditions that make shellfish unsafe for human consumption. When this happens we impose an emergency (temporary) closure on the affected area. The emergency closure remains in effect until water quality returns to previous levels and shellfish have had time to naturally cleanse themselves of contaminants.
We prepare annual reports for every growing area that summarizes the previous year's data and the area's classification status. We also prepare early warning system summary reports for each county that identifies where water quality is impacted and may require a change to the commercial growing area classification. These reports are accompanied by an Annual Inventory Map (PDF).
Water Quality Data
Contact us to request preliminary water quality data.
About the Program
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