3. Defining and describing the water environment
This section explains how the Environment Agency describes the water environment geographical units, and how we assess their current condition.
The WFD Regulations cover all waters, including inland surface waters, groundwater, estuaries and coastal waters, independent of size and characteristics.
For the purpose of implementing the WFD Regulations, waters are assigned to geographical or administrative units: the river basin, river basin district and water body.
The river basin is the area of land from which all surface run-off flows through a sequence of streams, rivers and, possibly, lakes into the sea at a single river mouth or estuary.
The river basin district is the main unit for management of river basins under the WFD Regulations. River basin districts in England were identified by the Secretary of State in 2003. A river basin district includes the area of land and sea made up of one or more neighbouring river basins together with their associated groundwater and coastal waters.
Water bodies are the units used for reporting and assessing compliance with the principal environmental objectives of the WFD Regulations. The environmental objectives apply to water bodies and so the main purpose of identifying water bodies is to enable status to be accurately described and compared to the environmental objectives set out in the WFD Regulations.
The WFD Regulations (Schedule 1) define a surface water body as a ‘discrete and significant element’ of surface water such as a lake or reservoir or entire (or part) stream, river or canal, estuary or stretch of coastal water (out to 1 nautical mile, and for chemical status only, this extends to the limit of territorial waters which may extend up to 12 nautical miles).
A groundwater body is a distinct volume of groundwater within an aquifer or aquifers.
Water bodies in England were first identified as part of a ‘characterisation’ process in 2003.
Water body categories, such as groundwater or coastal waters, are delineated as a discrete area and are shown as this total area for reporting purposes.
Whilst all lengths of river, stream or drainage channel in the defined catchment areas of a water body are protected and managed, reporting uses a river line within that catchment derived from the ‘detailed river network’. This river line is purely a reporting network and it is this river line which appears on maps in the river basin management plans.
The WFD Regulations cover all bodies of surface water. Where a stretch of water is too small to be formally identified as a water body, or is too small to show up on a map of the water body, it is still protected by law from pollution, modification and abstraction and can still be improved where local actions and assessments deem it to be a priority.
3.1.1. Using catchments for river basin planning in England
Taking a catchment based approach helps to bridge the gap between management planning at river basin district level and activity at the local water body scale. The catchment scale is large enough to add value at a strategic level but small enough to encourage local scale engagement and action.
In England, each river basin district is divided into management catchments to facilitate presentation of data and information. These are large catchments with many, often interconnected, water bodies. They are based on the catchments used for managing the availability of water for abstraction and flood risk management.
These management catchments have been further divided into operational catchments covering a small number of water bodies (typically 1 to 10) based around the same local geography or sharing specific pressures. Economic appraisals have been based on operational catchments.
3.1.2. Surface water body types and reference conditions
The sorts of animals and plants found in upland, rocky, fast-flowing streams are naturally very different to those found in lowland, slow flowing, meandering rivers. Therefore, to predict the animals that would be found in undisturbed or high status surface water bodies, they are grouped into different types according to their physical and chemical characteristics.
Descriptions covering the sorts of plants and animals expected to be found in the different types of water bodies in undisturbed conditions have been produced for each type or group of types. These types are the ones that have been used in the characterisation of each river basin district. In some cases, there are no sites in reference condition in the United Kingdom and descriptions are based on similar types in other European countries, extrapolation from modelling studies, or historic data or expert opinion (or both). For some methods more detailed site-specific reference conditions have been used.
Reference conditions and the conditions found in high status waters are the same. The Ministerial directions on environmental standards give the values for high status for biological and physico-chemical elements and include screening approaches for high status hydrology and morphology. To be in overall reference condition or high status, a water body needs to comply with all the criteria monitored: biology, physico-chemical, hydrological regime, morphological and chemical criteria.
3.2.1. Protected areas
Protected areas are parts of the environment requiring special protection for the protection of their surface water and groundwater quality or for the protection of habitats and species directly dependent on water. The Environment Agency has monitoring programmes in place for assessing compliance for Bathing Waters (under the Bathing Water Regulations 2013) and, under WFD Regulations, drinking water protected areas. The Environment Agency monitors some attributes for water-dependent habitats sites, but Natural England is responsible for assessing and reporting status for these sites. The Food Standard Agency’s food hygiene classification monitoring is used to assess compliance for shellfish water protected areas. Other information can be used to assess compliance in protected areas including conceptual models and modelling data, some of which are from third parties such as water companies.
3.2.2. Water body status monitoring
Monitoring sites are used to establish the status of water bodies in terms of their ecology, chemistry, hydromorphology and groundwater level.
In surface waters, a small network of surveillance monitoring sites is used to provide information on long-term natural and anthropogenic trends. In rivers and lakes an additional operational monitoring programme is used to classify water bodies according to the pressures acting on the environment. In coastal and estuarine waters the operational monitoring programme has traditionally focussed on two priority pressures, nutrients and chemicals from point source discharges.
A groundwater quality monitoring network meets the monitoring requirements for chemical status and trend assessment. A groundwater level monitoring network is used to meet the requirements of quantitative status assessment.
3.2.3. Assessment of water body status
Water bodies are assessed by classifying data collected from monitoring and, if appropriate, other sources. A classification will show whether the quality of the environment is good, or where it may need improvement. The assessment is used for long-term planning purposes, so it is important to make an assessment that is representative of status over a long period of time, rather than an assessment based on intermittent conditions that have no long-term significance.
Classification assessment is done on a range of quality elements relating to the biology and chemical quality of surface waters and quantitative and chemical quality of groundwater. To achieve good ecological status or potential, good chemical status or good groundwater status every single element assessed must be at good status or better. If one element is below its threshold for good status, then the whole water body’s status is classed as less than good.
Classification is just one part of the evidence base that helps to focus efforts on those water bodies where improvement measures might be needed. Additional information is sometimes required to assess whether a classification result is really indicative of an environmental problem; this is known as a weight of evidence approach. Additional evidence may also indicate where problems exist which are not apparent through classification results alone.
For surface water bodies there are two separate classifications: ecological and chemical.
Chemical status
The approach to chemical status has changed since 2015 and now a more advanced and sophisticated approach to classification is used. This helps to more accurately reflect the accumulation of some of the more persistent substances (termed ubiquitous, persistent, toxic and bioaccumulative or uPBT substances), which can be underestimated by monitoring water alone.
Biota environmental quality standards (concentrations in aquatic animals) are used to assess uPBTs. These biota standards protect both wildlife and people from harmful substances that can accumulate through the food chain. Concentrations are measured of these substances in fish, crustaceans (signal crayfish) and molluscs (blue mussel).
The biota monitoring network is small as it is neither practical nor ethical to extensively assess chemicals in biota. If uPBT substances are only classified in the specific water bodies where we do monitor biota, there would be little overall change in status and this would mask the significance of the results from the biota network. So the Environment Agency extrapolates the locations it monitors to represent much larger geographical areas for classification purposes.
For most uPBT substances it is not possible to predict concentrations in biota from water monitoring data. This means we are not able to use water monitoring as an alternative.
However, for perfluorooctane sulfonate (PFOS) it has been possible to establish a relationship between levels observed in river water and those in fish. Consequently, water monitoring data is used, where biota data is not available, to predict exceedance of the biota environmental quality standard in fish. As concentrations of PFOS are more locally variable than other uPBTs water quality models have also been used. These models have been calibrated using extensive environmental data from water industry chemical investigations where there are gaps in monitoring. The same approach has also been adopted for cypermethrin (an insecticide).
Biota environmental quality standards assess substances that have accumulated in animals over long durations, so we also apply maximum allowable concentrations in water, when available, to protect wildlife over short exposure periods. This is particularly significant for poly aromatic hydrocarbons (PAHs) in estuaries.
Three groups of global pollutants cause the significant change in chemical classification:
- polybrominated diphenyl ethers (PBDEs are brominated flame retardants present in commercial products)
- mercury
- PFOS
PFOS belongs to a large, diverse group of man-made substances known collectively as per-and polyfluoroalkyl substances (PFAS). There are potentially several thousand PFAS currently in use around the world. They are sometimes called forever chemicals because of their extreme persistence in the environment. Because of their non-stick, water repellent and oil resistant characteristics, they have been used in the production of a very wide range of products including cooking utensils, stain-proofing textiles, food packaging and fire-fighting foams.
These results are not unexpected as other countries around the world report similar levels of these substances. Although these chemicals are all now controlled, they have been widely used in our homes and businesses in the past. There are international agreements to reduce emissions but because these chemicals persist and do not break down quickly, they will be in the environment for decades to come.
There is little underlying change in chemical status for other substances. If these three global pollutants are excluded together with polycyclic aromatic hydrocarbons which are significant in estuaries and cypermethrin, which is included in our assessment of chemical status for the first time, about 97% of water bodies still achieve good chemical status.
The maps of chemical status can be viewed with and without uPBTs on the river basin management plan mapping system to show the impact of these changes.
For groundwater bodies there are two separate classifications: chemical status and quantitative status. In addition to assessing status, there is also a requirement to identify and report where the quality of groundwater is deteriorating because of pollution, which may lead to a future deterioration in status.
Considering wider evidence of an environmental problem
As noted earlier, classification is just one part of the evidence available on the condition of the water environment. Additional information is sometimes required to assess whether a classification result really indicates an environmental problem in a water body.
For surface waters the certainty that an element or water body is at less than good status is expressed using the 3 categories of very certain, quite certain and uncertain. These definitions are based on statistical certainty from analysis of the monitoring data used to derive the classification results: very certain (greater than or equal to 95%), quite certain (greater than or equal to 75% less than 95%), uncertain (greater than 50% less than 75%).
The level of certainty that an element is at less than good status can influence the justification of the measures needed to resolve the problem. In general, justifying costly or targeted regulatory measures requires a higher degree of certainty that there is a problem than is needed to justify low cost, voluntary type measures. This reflects the relative risk of wasting resources and investment in taking unnecessary action.
Classification and statistical certainty derived from operational monitoring may be unable, on their own, to provide the certainty needed to justify the measures required, particularly if the failure is caused by pollution from diffuse or intermittent sources. In these cases, additional evidence is used to make a pragmatic, qualitative judgement of the certainty that there is a problem to solve, based on a weight of evidence approach. This additional evidence could come from pollution incident or investigative monitoring data or from a catchment-scale assessment of available evidence and information.
The classification results provide part of that weight of evidence, but it is important to note that the additional weight of evidence approach to improve certainty that there is, or is not, a problem to solve does not over-ride the formal classification result.
Weight of evidence assessments for nutrients and eutrophication
Eutrophication is when there is too much nutrient in waters, causing algae and plants to grow excessively. This affects the quality of the water and how it can be used, as well as damaging the local wildlife.
The nutrient standards used for water body status classifications are based on an understanding of the links between nutrients and the biological impacts associated with eutrophication. There is uncertainty in the ability to use this knowledge to predict the impacts in particular water bodies; exceeding the nutrient standard alone is considered insufficient to judge the risk of impacts on the biology. As a result, the Environment Agency uses a weight of evidence approach in assessing eutrophication and targeting control measures.
The one-out-all-out principle for water body status classification means that if nutrients are at less than good status then a water body is classed as moderate status, regardless of whether the biology is less than good status. Using the weight of evidence approach the Environment Agency assesses the evidence of the nutrients and also their impacts, using the plant and algal quality elements sensitive to nutrients and the certainty that these are, or are not, less than good status. Wider evidence of eutrophication, for example, from investigations, is also taken into account, including information from partners, to increase certainty. This assessment, of certainty of eutrophication, does not affect the classification result but informs decisions on subsequent measures as described above, with high certainty being required if costly targeted regulatory measures would be needed to address the problem. This approach makes best use of the available evidence and provides a link between standards, classification, investigations and measures.
The Environment Agency has developed eutrophication assessments for water bodies at risk from nutrients in rivers, lakes, estuaries and coastal waters. These assessments have been used in targeting the measures to tackle nutrients in the river basin management plans. They are particularly important to the targeting of expensive regulatory measures such as phosphorus reduction at sewage treatment works.
A new nitrogen standard has been developed for lakes and was used to classify total nitrogen in lake water bodies for the first time in 2019. However, there are concerns about the relevance and application of this new nitrogen standard to some types of reservoirs, particularly ‘concrete bowl’, pumped storage reservoirs used primarily for public water supply. The Environment Agency will, therefore, review the use of the nitrogen standards for this type of reservoir before the next update of the river basin management plans in 2027. In light of the uncertainty of the appropriateness of the nitrogen standard for these reservoirs, where total nitrogen is reported at less than good status, water companies will be asked to undertake initial scoping studies of nitrogen sources and the feasibility of reducing inputs, rather than developing schemes for inclusion in the next water industry price review.
Where an element is classified as being at less than good status, an assessment is needed of the measures that could be taken to improve the status to good. In order to identify appropriate measures, it is first necessary to understand the cause of the failure.
The cause is recorded using a defined set of reasons, consisting of 3 pieces, or tiers, of information:
- tier 1: significant water management issue, for example, diffuse source, point source or physical modification
- tier 2: more detailed activity or source, such as arable field, sewage discharge (continuous) or flood protection structures
- tier 3: sector, for example, agriculture and rural land management, water industry or Environment Agency
Where a biological element is at less than good status the pressure, for example ammonia or sediments, causing the failure is also identified, with the associated reason.
If more than one reason for not achieving good status is identified for a failing element (or for a pressure affecting a biological element) then the source apportionment of each reason is also recorded. So, if there are two sources of ammonia, a diffuse source and a point source, then the relative contribution of each source to the overall ammonia problem is recorded.
A level of certainty (suspected, probable or confirmed) is also assigned to each reason for not achieving good status, based on a weight of evidence approach.
For ‘suspected’:
- there is some information that points to a possible reason for not achieving good status
- further investigations are required before site specific measures can be identified
- part of the source-pathway-receptor linkage is missing, for example, a probable source and receptor has been identified but the pathway is not established
For ‘probable’:
- there is reasonable evidence that points to the reason for not achieving good status
- further investigations are required before site specific regulatory or expensive measures can be considered
- the source-pathway-receptor linkage has been established with reasonable certainty. There is reasonable evidence which generally give a consistent (that is, not contradictory) picture
For ‘confirmed’:
- there is compelling evidence for the reason for not achieving good status. The available evidence should demonstrate cause and effect in a way that would be compelling to all partners
- no further investigations into the reasons for not achieving good status are required before site specific regulatory or expensive measures can be justified
- the source-pathway-receptor linkage has been established. There is good evidence which gives a consistent (that is, not contradictory) picture
Defining the problem in this way supports the appraisal of appropriate measures to address the problem. The source apportionment information informs the targeting of effort and where appropriate, the analysis of the costs and benefits of any measures.
The same approach is used for recording reasons for deterioration.
You can view a summary of the reasons for not achieving good status and reasons for deterioration for water bodies on the challenge data pages on catchment data explorer.
3.4.1. Risk assessments
The WFD Regulations require the pressures acting on each water body to be identified. This can mean any pressure that on its own, or in combination with other pressures, represents a risk of failure to achieve the environmental objectives of the river basin management plans.
Risk assessments produced for the 2009 plans were reviewed for the 2015 update to the plans and, where new data and information was available, the risk assessments were updated.
These risk assessments have been reviewed again for this update to the plans but having been assessed as appropriate they have not been changed. The Environment Agency has published the methodologies and results for these risk assessments alongside the 2015 river basin management plans.
3.4.2. Managing risk
Risk information was used to optimise the design of the monitoring programmes. Many other aspects of catchment scale planning are also partly informed by the water body risk assessments, for example, informing whether failure to achieve an objective is due to an environmental problem, and to help design monitoring programmes.
Risk information has also been used by catchment partnerships in developing the catchment level programme of measures. Catchment partnerships used the Environment Agency future predicted pressures, alongside their local knowledge to consider what actions and measures would be needed to mitigate future challenges. The future challenges, actions and measures of the catchment partnerships can be seen in the catchment partnership pages on catchment data explorer.
Feedback from catchment partnerships and others through the Challenges and Choices consultation has highlighted the importance of improving the management of risk. As part of this updated plan there are proposals to work collaboratively with partners to develop shared approach to understanding existing and emerging risks. A shared understanding of current risks and future status will be hugely important if partners want to work together in a complementary way to reduce risks to the water environment at national and local levels.