Water Environment and Water Services (Scotland) Act 2003 implementation - assessing Scotland's water environment: policy statement

5. Levels of Confidence

In any system for classifying the state of the environment there will inevitably be uncertainty. This may lead to some water bodies being misclassified. Some of the uncertainty will result from the limited amount of monitoring data that SEPA has been able to obtain using the new monitoring and assessment methods before the first classification results had to be produced. Over time more data will be gathered, and this will help reduce uncertainties.

Before action to improve water bodies is taken, we need to be confident that there really are adverse impacts to be addressed: where water bodies have been classified as worse than good, we need to be confident in that classification. Accordingly we expect SEPA to provide information on the confidence of its classification for each water body. This information will be important in identifying any appropriate follow-up action.

To do this, SEPA should, in accordance with the 2024 Status Directions, identify the confidence of class in respect of the results for each quality element (or test in respect of groundwater classification) that was assessed in order to make the classification decision. It should define the confidence as either “high”, “medium”, or “low”.

In making an assessment of confidence, SEPA may take into account a range of sources of evidence about the impacts on a water body. Such evidence may include suitable data provided by other organisations. The process developed by SEPA must be transparent in order to demonstrate what evidence has been considered and the results of those considerations.

This assessment of confidence informs SEPA and other regulators' decisions about where to prioritise action, in line with the principles set out in section 2 above.