Priority river (including streams) and lake habitats are defined at UK level, with responsibilities for their conservation devolved to country-level (England, Wales, Scotland and Northern Ireland). A full list of UK definitions of priority habitats is provided here, along with further explanation of the UK’s commitments. The original UK Biodiversity Action Plan has been superseded by individual delivery strategies in the different parts of the UK. The strategy covering 2010-20 was called Biodiversity 2020. DEFRA is currently working on a strategy for 2020-30.


This river belongs to two types in the UK BAP definition: chalk rivers and type H3260 (Image NE)

Priority river habitat

When UK priority habitats were originally defined only one river habitat was included – chalk rivers. In 2008 and following extensive consultation, other river types were included in an expanded priority river habitat definition – headwater streams, active shingle rivers and watercourses with Ranunculion Fluitantis and Batrachion vegetation (Habitats Directive river habitat H3260). In addition, under the revised definition any river or stream containing a priority species is also eligible to be considered as priority river habitat. The combination of these changes greatly extended the scope of priority river habitat, effectively encompassing the entire river and stream network, and triggered the need for a rethink of how to approach its conservation (see explanation below).

Priority lake habitat

Oligotrophic and dystrophic lakes, mesotrophic lakes, eutrophic standing waters and aquifer-fed naturally fluctuating water bodies are all specific priority habitat types. Generally if a water body is larger than 2 hectares it is considered a lake, whereas if it is smaller it is considered a pond (although in reality the cut-off is not strictly applied). Ponds are also a priority habitat type, but ponds are not considered on this webpage – see the Freshwater Habitats Trust webpage for information on priority pond habitat.



Approach to conserving priority freshwater habitats in England

Naturally functioning freshwater habitats support species rich wetlands (Image N. Lumsden)

The aim is to protect our most natural remaining examples of freshwater habitats, and restore as much natural function as possible to the rest of the freshwater habitat resource. Natural habitat function, based on natural hydrological, chemical, physical and biological processes, generates diverse, sustainable and resilient freshwater ecosystems in which our freshwater wildlife can thrive. All of our native freshwater species have evolved to exploit niches in naturally functioning rivers, streams, lakes and ponds. Naturally functioning freshwater habitats can also support our wetland habitats and species, and help provide the connectivity they need.

The concept of natural ecosystem function has strong synergies with the objectives of the Water Framework Directive (the European legislation covering management of the water environment), as well as freshwater habitat objectives for specially protected sites (Special Areas of Conservation, notified under the European Habitats Directive and Sites of Special Scientific Interest, notified under UK law).

Further explanation of the biodiversity importance of natural habitat function in freshwaters, and the role of priority habitats in protecting and restoring natural function, can be found in this freshwater and wetland habitat narrative. This narrative is in line with Natural England’s rationale for conserving Special Areas of Conservation and Sites of Special Scientific Interest notified for their freshwater habitat. It has also been used as the basis of biodiversity guidance for restoring the ecological status of water bodies under the Water Framework Directive.


Protecting natural function 

Our most naturally functioning freshwater habitats are those with:

  • water chemistry that is not impacted by pollution;
  • natural morphology and dynamic physical processes shaping habitat mosaics;
  • a natural hydrological regime not impacted by abstraction, diversion, effluent discharge, drainage and impoundments;
  • natural biological assemblages with a lack of invasive non-native species or other direct biological manipulations such as fish species removals and stocking.

Standing waters of artificial origin can still function naturally and consequently can still be considered naturally functioning if they possess the characteristics above.

Headwater streams are under-protected, but vital natural functioning habitats (Image NE)

Rivers, streams and lakes which function in this way are considered to be ‘priority habitat’. Priority habitat maps for rivers/streams and lakes have been produced, but this has, by necessity, been based on partial data sets, which is why we want your help.

Further explanation of the biodiversity importance of natural habitat function in freshwaters, and the role of priority habitats in protecting and restoring natural function, can be found in this freshwater and wetland habitat narrative


What difference does being labelled ‘priority habitat’ make?

Being recognised as priority habitat provides an additional mechanism to protect and enhance the habitat. In England, the strategy ‘Biodiversity 2020’ currently governs action on priority habitats and species, but a new Nature Strategy is currently being developed under Defra’s 25 year environmental plan to follow on from this.

Artificial incision (a consequence of gravel extraction) of the channel reduces naturalness and impacts function (Image NE)

The priority habitat maps are used by Natural England, the Environment Agency and planning authorities to highlight where decision-making needs to take particular account of habitat naturalness, for instance in the targeting of agri-environment measures and the consideration of planning applications and flood defence permits.

The maps can also be used in planning any restoration measures to enhance and extend natural habitat function. For instance, the Freshwater Habitats Trust is generating maps of freshwater biodiversity hotspots, which can be used in conjunction with priority habitat maps to understand where recolonization of restored habitat may be quickest and most comprehensive (in terms of natural species complement).


Mapping priority freshwater habitats in England

Current version of the priority river habitat map  (Image NE)

Priority habitat maps have been generated for rivers/streams and lakes which seek to capture the remaining highly natural examples in England. These are based on nationally available data, which largely relate to larger rivers and lakes that are monitored for Water Framework Directive purposes. Considerable work is needed to understand the naturalness of streams and small lakes across England to complete the picture. Some initial local refinement has been undertaken on the river map but this has largely related to removing larger rivers where the national data analysis has generated spurious judgements of naturalness. You can view the current versions of the priority habitat maps for rivers/streams and lakes here.


Mapping types

New maps of the distribution of river/stream types included in the UK BAP definition of priority river habitat are being developed and will be displayed on the Display rivers/stream types data tab as and when they are ready. An updated map of chalk rivers has already been produced and is now available to view- an explanation of how this was produced can be found here. (A downloadable version of the layer is now available from Natural England’s ARCGIS online facility here). Proposals for local refinements to the layer can be made via your local catchment partnership or directly on the Data Portal. A UK-level modelling exercise is being conducted to generate predictive maps of Habitats Directive H3260 rivers, active shingle rivers and other river and stream types relevant to the European Red List of Habitats– an explanation of the modelling work will be available here soon.

Mapping restoration priorities

Existing nationally generated maps of river/stream and lake restoration priorities are now being refined with stakeholders to become a mechanism for highlighting local priorities for different sorts of restoration of natural habitat function – hydrological, physical, chemical and biological. Any site that falls under the UK river and lake priority habitat definitions (which essentially means any river, stream or lake), and therefore warrants specific consideration, can be highlighted as a priority for restoration action, if the action restores natural function. See the new facility on the data portal for how to get involved in this work. You can see how the maps of restoration priorities are developing by accessing the display data facility.


Assessing the condition of priority freshwater habitats

Provisional portrayal of naturalness in headwater streams (Image NE)

England-wide assessments are made of the condition of priority habitats at regular intervals. Work is being done to generate a more coherent assessment framework for priority freshwater habitats, based on naturalness and natural habitat function across the whole freshwater habitat resource. This will draw on information from various sources such as Environment Agency monitoring, protected site condition assessment and citizen science (from this website and others such as CaBA). Assessment will be made of key components of naturalness.natural ecosystem function (physical, hydrological, chemical and biological), using a 5-class classification from very high to very low. Further information on the proposed framework can be found here. The work is now being taken forward as part of Defra’s 25 Year Environment Plan indicator framework, via indicator B6 (natural functions of water and wetland habitats). A recent progress report on the B6 indicator can be found here.



Targets for priority freshwater habitats

New biodiversity targets for freshwater and other habitats are being developed under the Environment Act and Defra’s emerging strategy for nature. To inform this, work is being undertaken to develop naturalness targets for freshwater and wetland habitats, based on the proposed assessment framework outlined above, which will provide the basis for restoring more natural function to our freshwater habitat resource. These will be linked into water targets aimed at improving the aquatic environment, in order to harness the combined strength of biodiversity and water objectives.

Your involvement in refining the priority habitat maps is vital in ensuring we protect the most natural remaining freshwater site we have and in stimulating restoration action in the wider freshwater habitat resource. See the Contribute Data tab to see how you can help.