Reasons for shellfish harvesting area closures
Learn about why harvesting areas are sometimes closed to the public.
On this page
- About area closures
- Poisoning from contaminated shellfish
- Contamination and water quality
- Weather events
- Related links
About area closures
Eating contaminated bivalve shellfish can be harmful or even fatal. Clams, oysters, scallops and mussels can be contaminated by toxins, bacteria or chemicals in surrounding waters. Before harvesting bivalve shellfish, ensure that the area you plan to use is open and approved for harvesting.
Areas that exceed the allowable limits of any harmful substance are closed to shellfish harvesting.
We communicate shellfish harvesting closures through:
- the shellfish harvesting map
- area closure signs
- the regional shellfish harvesting closures websites
- direct communication with bivalve shellfish harvesters, processors and local media
Poisoning from contaminated shellfish
Shellfish feed by filtering microscopic particles, such as algae, from the water. Some types of algae can remain in the shellfish and cause harmful effects to humans if they are consumed. Canada closes shellfish areas affected by these harmful algal blooms to prevent human illness.
Contamination and water quality
Where shellfish are present, the water quality can be contaminated from human activities and natural processes, such as:
- failing residential wastewater systems
- municipal wastewater treatment systems
- industrial facilities discharging into the environment
- runoff from land, like in the case of agricultural activities, which makes the source hard to identify and measure
Waste from these activities and processes may contain harmful bacteria and viruses that make shellfish dangerous to eat, such as:
Eating contaminated shellfish can cause serious health issues such as hepatitis A, typhoid fever, mild diarrhea and vomiting.
As a result, a shellfish harvesting area is closed if there is a possibility that the shellfish are contaminated from these activities and processes.
Testing harvesting areas
The Government of Canada tests the waters where shellfish are harvested for bacteria. If bacterial levels in the water sample exceed safe guidelines, the area is recommended for closure.
In addition to collecting water samples, the federal government also evaluates the potential sources of water contamination close to these shellfish harvesting areas. When there is a distinct possibility of contamination, we evaluate the threat closely. We provide additional recommendations to either fix the issue and/or close the area to shellfish harvesting.
Closures are common around urban areas where there is the possibility of contamination from marinas and wastewater systems.
Shellfish harvesting areas may be closed because of weather related events, such as melting snow, heavy rainfall or flooding.
A rainfall warning is issued when heavy or prolonged rain causes flooding. Heavy rains can cause:
- contaminants on land to runoff into the water
- sewage treatment systems to overflow, resulting in untreated wastewater going directly into the water where shellfish live
An affected shellfish area must be closed immediately to all harvesting. The area remains closed until the effects of the rainfall have disappeared. At that point, it is assumed that shellfish are again safe for human consumption.
Because of this increased risk from the weather, shellfish areas are closed to harvesting if needed. The risk depends on a number of factors, including:
- time of year (season)
- historical information of the area
- weather conditions before a storm
- trends in the freezing and thawing cycle
- amount, duration and intensity of rainfall
- likelihood of flooding and sewage overflows
- how much the soil can absorb the rain (ground saturation)
- what the surrounding land is used for (local land use activities)
How shellfish harvesters can prepare for a weather-related closure
Shellfish harvesters should monitor weather forecasts for weather events and rainfall warnings. Information sources include:
- weather broadcasts by local media outlets
- public weather alerts for Canada
- recorded telephone weather forecasts and warnings
- hurricane bulletin e-services available by email, Twitter or web feed
Communicating closures and openings
The federal government communicates openings and closures related to emergency and non-emergency weather events by:
- news release
- fishery notice
- telephone call
- mapping application website update
Contact your local Fisheries and Oceans Canada office to receive automatic notifications.
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