Shellfish water monitoring

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​About monitoring shellfish waters

Monitoring the seawater around Jersey’s aquaculture beds is important​ to:

• collect background environmental data
• detect long-term pollution trends
  
• assess compliance with the EU Water Framework Directive (WFD)
• provide valuable information to marine users and the aquaculture industry

Shellfish b​eds in Jersey

Shellfish cultivation takes place along the southeast coast of Jersey in Grouville Bay, covering around 7 hectares of intertidal zone. This area is dedicated to farming oysters and mussels.

Why monitoring shell​fish waters matters

Coastal waters are influenced by both natural processes and human activity, which can affect the health of shellfish. Oysters and mussels are filter feeders. This means they draw water through their gills, trapping food particles.

This feeding method makes them highly vulnerable to pollution, as contaminants in the water can be ingested in the same way as food.

Ensuring safety and quality

Regular monitoring of coastal waters helps safeguard both the shellfish and the people who consume them.

By checking water quality and shellfish health, we ensure that aquaculture products remain safe to eat and that the marine environment is protected.

For more details and guidance on fish and shellfish regulations and monitoring​.

Setting Standards

Water quality data is compared against benchmarks established by the EU Water Framework Directive.

While the Directive is not legally binding in Jersey, it provides a valuable framework for maintaining high environmental and food safety standards in our shellfish-growing areas.

Learn more about the Water Framework Directive on the Eu​ropean Commission website.

How our shellfish waters are tested

We test chemicals on-site quarterly. The data we collect includes:

• pH
• dissolved oxygen
• salinity
• temperature​
  
• suspended solids
• bacteria

Heavy metals are tested twice per year.   

The results are compared against EU Directive standards - EU Water Framework Directive 2000.​

Shellfish waters monitoring report 2015 to ​​2024

The results of the water quality monitoring are compiled into a report, that aims to provide a detailed summary of the results from 2015 to 2024.

Monitoring of Jersey shellfish waters repor​t 2025

Overview of current results 2019 to 2025

The Water Framework Directive (WFD) uses annual averages to determine if parameters being tested breach the Environmental Quality Standards (EQS).

It uses 6-year averages to determine a water body’s chemical status.  The overall status uses the ‘one-out-all-out’ principle, determined by the parameter with the lowest status. 

4 new parameters were added in 2025:

• calcium
• chromium (v)
• chromium (III)
  
• organic carbon
  

The annual averages show that the individual parameters tested in Jersey’s shellfish waters generally meet  ‘good status’, when compared to the EQS’s set by the WFD. This is the same for the 6-year average.

However, 6 yearly average results for zinc and lead are consistently above the EQS at all sites.  Along with the new parameter Chromium (v), also detected above the EQS in 2025 (this result is being checked by the laboratory). Therefore, they do not fulfil the requirement to achieve overall ‘good status’, despite most of the individual parameters being below the required EQS.

It is important to note that the laboratory limits of detection for zinc and lead have improved over time.  The high limits of detection have artificially elevating historic levels leading to EQS breaches.  This is demonstrated in results from 2025 where zinc and lead are below their EQS.​

6-year average results tables for 2020 to 2025​

​Parameters that are below their target level

​Parameters that are above the target level

P​arameters where the limit of detection is above the target level

Average annual results for ​2025​

These results demonstrate improvement in laboratory LOD. All results were either at the LOD or below the EQS.​​

Parameters that were below their target level​

Parameters that are below the limit of detection

Parameters where the limit of detection is above the target level