Environmental monitoring

Dissolved oxygen, salinity levels, temperature, pH and a number of other parameters are continuously monitored from 10 locations throughout the Bay. Readings are taken every 15 minutes – you can view the data on the:

Storm Central website

The Cardiff Bay Barrage Act states that dissolved oxygen levels must be maintained above 5 milligrams per litre throughout the Bay. This standard was set to protect migratory fish, such as salmon and sea trout, which travel through the Bay on their way to and from their breeding grounds further up the rivers. Salinity levels are measured to ensure that the operation of the Barrage locks and sluice gates minimises the volume of seawater entering the Bay. This is important to ensure that a freshwater environment is maintained. Water samples are taken on a regular basis and analysed for additional water quality parameters, including metal salts and nutrients.

Due to the presence of storm sewer overflows along the rivers Ely and Taff, the Bay receives water contaminated with sewage during periods of heavy rainfall. The Harbour Authority works closely with Cardiff Council’s public health team and Welsh Government health advisors to minimise the health risks to water users.

Water samples are taken weekly in the winter and twice-weekly in the summer to monitor levels of sewage-derived bacteria. The results have been used to develop a computer model, which is run on a daily basis to help predict the levels of potentially harmful bacteria in the water. The model predicts either ‘poor’, ‘good’ or ‘excellent’ conditions.

This information is sent to organisations who undertake activities in the Bay, so they can assess if they pose any health risks.

Latest predicted water quality forecast

All of the results from the Harbour Authority’s water quality monitoring programme are analysed, interpreted and presented in a quarterly report.

View the latest Water Quality Report