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

3. Classification Schemes

3.1 Overview

In addition to the introduction of specific standards and condition limits, we need a mechanism for assessing and describing where the water environment is of good quality and where it may require improvement. Classification systems provide such a mechanism for describing the state of our aquatic environment and for assessing the effectiveness of our programme of measures in achieving the environmental objectives established in the river basin management plans.

This section describes the classification schemes and how they are being applied as part of the river basin management planning process, including:

• how the environmental standards and condition limits set out in the 2024 Standards Directions should be used for the purposes of classification;
• how SEPA should carry out an assessment of its confidence in the classification results; and
• how the results of the classification exercise should be presented and reported.

The classification schemes have been introduced, via Status Directions to SEPA, in respect of:

• surface water bodies (section 3.3)
• groundwater bodies (sections 3.4)
• surface water bodies designated as heavily modified or artificial (section 3.5).

The application of these schemes has provided us with our most comprehensive assessment of the status of Scotland’s water environment. Information on the results of classification is available on SEPA's website^[3].

3.2 Using monitoring to inform classification

Each water body is classified by determining the impacts of the pressures to which it is subject using data collected by monitoring and, where relevant, the results of modelling.

As discussed at section 1.2, SEPA has established a risk-based monitoring programme and must continue to collect sufficient data to inform its classification decisions. SEPA is expected to provide information on its confidence in its classification (see section 5 below).

For the purposes of classification, SEPA may discount monitoring results which are influenced by one-off, unrepresentative and transient incidents, provided that the condition of each affected water body is adversely affected for only a short period of time (i.e. there is only a transient blip in the condition of the water body).

3.3 Classification of surface water bodies

WEWS and its associated regulations require each surface water body to be classified in terms of its ecological and chemical quality. For those water bodies not designated as heavily modified or artificial, this ecological quality is described in terms of ‘ecological status’. This is an expression of the quality of the structure and functioning of surface water ecosystems as indicated by the condition of a number of ‘quality elements’. The term ‘quality elements’ refers to the different indicators of ecological quality making up its ecological status classification schemes.

There are five classes of ecological status, defined in terms of how much the ecological quality deviates from natural conditions. These are high, good, moderate, poor or bad. High status means that the water body is unaffected or virtually unaffected by human activity. A good status water body shows some signs of human pressures, such as slight alterations in the composition or abundance of water plant or animal communities (biological quality elements) compared with what would be expected in a water body at high status.

The quality elements used to assess ecological status are:

• biological quality elements (water plants and animals);
• chemical and physicochemical elements (eg oxygen and nutrient levels); and
• hydromorphological quality elements (water flows and levels; the condition of beds, banks and shores; and the continuity of rivers for fish migration).

For good status, the chemical, physicochemical and hydromorphological quality of the water body must achieve the standards and conditions necessary for the biological quality elements to be in good condition. The ecological status of a water body is determined by the lowest-classed quality element. This is called the ‘one-out, all-out principle’.

Chemical status is either ‘good’ or ‘failing to achieve good’. ‘Good’ means that none of the environmental quality standards established for priority substances and other dangerous substances identified at EU-level is being exceeded.

Ecological status and chemical status are then combined to provide an assessment of overall surface water status. The following diagram illustrates how these various elements are combined and how the ‘one-out, all-out’ principle is applied.

The relevant quality elements for classifying a particular water body depend on whether the water body is a river, loch, estuary or coastal water body. Standards and condition limits define the class boundaries applicable to the different quality elements and these are set out in the 2024 Standards Directions.

Biological monitoring systems for measuring the ecological impact of abstractions, flow regulation and engineering works are in development. Until these tools do become available, SEPA will continue to classify the ecological status of surface water bodies by comparing their hydromorphological conditions with the hydrological and morphological standards and condition limits set out in the 2024 Standards Directions. Whilst moderate impacts from water abstractions or flow regulation will be factored into classification through the use of flow standards, a classification of poor or bad will only be assigned where there is ecological evidence of severe impact from a set of ecological indicators.

Spatial considerations

An important factor in assessing the status of a water body is the spatial extent of any adverse impact on a water body. Failures of environmental standards over a limited spatial extent in a water body, although causing ecological damage, will not individually be expected to affect the ecological status of the water body as a whole. In contrast, failures of standards that individually or cumulatively extend over a significant area or length of a water body will affect the body's ecological status and must be reflected in the classification results.

To ensure that classification results reflect impacts on the ecological quality of the water environment that are of sufficient spatial extent to affect ecological status, SEPA will apply the spatial environmental standards in the 2024 Standards Directions.

To do this, SEPA should aim to ensure that the monitoring data and modelling results it uses in classification are representative of the appropriate spatial extents of water bodies as set out in the 2024 Standards Directions.

Invasive non-native species assessment

It is important to ensure that the impact of invasive non-native species is properly reflected in the classification process. Where significant adverse impacts are causing the ecological status of a water body to be moderate, poor or bad, we expect these to be reflected through the normal application of biological monitoring and assessment methods.

SEPA will take account of the impact of those ‘high impact’ species listed in the 2024 Status Directions. Where there is evidence that a listed species has become established over a significant spatial extent of a water body, SEPA will not classify the water body as being at high ecological status.

3.4 Classification of groundwater bodies

Protection of our groundwater resources is important to enable their continued use for public and private drinking water supplies, bottled water production and a range of other industrial uses. It is also important for our surface waters and wetlands which depend on the water that reaches them from groundwater.

For groundwater bodies, the approach to classification is different from that for surface water bodies. For each body of groundwater, we are required to classify its chemical status and its quantitative status. Both have to be classed as either 'good' or 'poor'.

Groundwater chemical status indicates whether or not:

(a) any pollutants in groundwater are causing:

• harm to surface waters into which the groundwater eventually flows;
• damage to wetlands that depend on the groundwater for their water needs;
• deterioration of the quality of water being abstracted (or planned to be abstracted) from the water body for human consumption;
• significant impairment (e.g. because of widespread pollution) of the ability of the groundwater body to support other uses;

(b) salty water at the coast or polluted water is being drawn into the body of groundwater to replace abstracted water

Groundwater quantitative status indicates whether or not any changes to groundwater flows and levels resulting from human activities, such as water abstraction, are causing:

• harm to surface waters that depend on groundwater flows during dry weather;
• damage to wetlands that depend on groundwater for their water needs;
• salty water at the coast or polluted water from neighbouring bodies of groundwater or surface water to be drawn into the body of groundwater; or
• groundwater levels to fall because (over the long-term) the rate of abstraction is greater than the rate at which groundwater is being replenished from rainfall.

The WFD sets out a series of criteria that must be met for a body to be classed as good chemical status and good quantitative status. These are further elaborated in the Groundwater Directive.

To classify bodies of groundwater, SEPA has to assess whether or not the relevant criteria are met. To do so, it is expected to undertake appropriate investigations where there are indications of a risk that one or more of the criteria for good status may not be met. The indicators of risk that SEPA is expected to consider are described in the 2024 Status Directions. With respect to groundwater chemical status, they include a series of threshold values. These are set out in the 2024 Standards Directions.

The ‘one-out, all-out’ principle described in section 3.3 also applies to groundwater classification; thus overall groundwater status is determined by the lower of the groundwater chemical status and quantitative status classifications. SEPA will be expected to classify the overall groundwater status of each body of groundwater as 'good' or 'poor' accordingly. These matters are elaborated in more detail in the 2024 Status Directions to SEPA.

3.5 Identification of water bodies designated as heavily modified or artificial

In some cases, substantial modifications to the physical characteristics of surface water bodies have been made to accommodate uses like navigation, water storage, flood defence and land drainage. Such modifications may be preventing the bodies achieving good ecological status. Where this is so and the bodies cannot be restored to ‘good’ ecological status without significant adverse effects on those uses, the water bodies have been designated as heavily modified bodies (HMWBs). Man-made water bodies, such as canals, that have been created where no natural water body previously existed, have been designated as artificial water bodies. The principal objective for such water bodies is to aim to achieve good ecological ‘potential’, at the latest by 2027. Further details of this process are described in our Policy Statement, “Principles for setting objectives for the River Basin Management Plan”.

There are five classes of ecological potential. The classes are defined in terms of how much the ecological quality of such water bodies deviates from the best that could be achieved (i.e. the maximum ecological potential) without putting in place mitigation (relating to the impacts of the modified or artificial physical characteristics) that would have a significant adverse effect on the relevant use or on the wider environment.

For the purposes of determining whether a heavily modified water body is at good or maximum ecological potential, SEPA cannot simply apply the normal standards and condition limits for hydromorphological quality elements or biological indicators that are sensitive to hydromorphological alterations. This is because a failure of these standards and condition limits would not necessarily mean that a water body was failing to achieve good or even maximum ecological potential. Instead, if all mitigation that could be taken to address the adverse ecological effects of a body's modified or artificial characteristics has been taken, SEPA is expected to:

(a) classify the water body's hydromorphological characteristics as being sufficient to enable the achievement of good or maximum ecological potential; and

(b) provided no other pressures (e.g. pollution pressures) on the water body are causing a failure of any of the standards or condition limits for 'good', classify the water body is achieving good or maximum ecological potential.

The classification of the ecological potential of heavily modified and artificial water bodies requires identification and assessment of the following:

• the modifications and artificial characteristics of the water body concerned that are preventing the achievement of good ecological status;
• the mitigation measures already taken in relation to those characteristics and whether they adequately mitigate the identified impacts;
• whether additional mitigation measures could be put in place without significant adverse effects on the use, or on the wider environment.

Water bodies affected by hydropower schemes

To avoid a significant impact on renewable electricity generation, SEPA will aim to achieve good ecological potential in water bodies affected by hydropower schemes over the three river basin management planning cycles to 2027 without a reduction in generation of more than around 100 GWh per year.

Most of the other steps in the process are similar or identical to those described in section 3.3 above for classifying the ecological status of other surface water bodies. In determining the appropriate mitigation measures, we expect SEPA to take into account the relevant guidance on good ecological potential published by UKTAG^[4],[5].

The classification of the chemical status of heavily modified and artificial water bodies follows the same process described in section 3.3 for other surface water bodies.

These matters are set out in more detail in the 2024 Status Directions.