Freshwater pearl mussels: advice for making planning decisions
Source: gov.uk (2025-04-07)

How to assess a planning application when there are freshwater pearl mussels on or near a proposed development site.

This is Natural England’s ‘standing advice’ for freshwater pearl mussels. It is a material planning consideration for local planning authorities (LPAs). You should take this advice into account when making planning decisions. It forms part of a collection of standing advice for protected species (https://www.gov.uk/guidance/protected-species-how-to-review-planning-applications#standing-advice-for-protected-species).

You should read this guidance alongside Protected species and development: advice for local planning authorities (https://www.gov.uk/guidance/protected-species-how-to-review-planning-applications).

Following this advice:
- avoids the need to consult on the impacts of planning applications on freshwater pearl mussels in most cases
- can help you make decisions on development proposals
You may need a qualified ecologist to advise you on the planning application and supporting evidence. You can find one using either the:
- Chartered Institute of Ecology and Environment Management (CIEEM) directory (https://cieem.net/i-need/finding-a-consultant/)
- Environmental Data Services directory (https://www.endsdirectory.com/)
How freshwater pearl mussels are protected

Freshwater pearl mussels are also protected under the Wildlife and Countryside Act 1981.

It is an offence to intentionally:
- kill, injure or take them
- possess or control them (or any part, alive or dead)
It is also an offence to intentionally or recklessly:
- damage or destroy a structure or place used for shelter or protection
- disturb them while they occupy a structure or place used for shelter or protection
- obstruct access to a structure or place used for shelter or protection
- possess or transport them (or any part, alive or dead)
- sell, offer, or publish an advert to sell them
Some freshwater pearl mussel populations are qualifying features of Special Areas of Conservation (SACs), and therefore receive further legal protection under the Conservation of Habitats and Species Regulations 2017. You can read on the Joint Nature Conservation Committee’s (JNCC) website which SACs have freshwater pearl mussels as a qualifying feature (https://sac.jncc.gov.uk/species/S1029/).

Freshwater pearl mussels are listed as critically endangered on the consolidated list of red listed species on the Joint Nature Conservation Committee’s website (https://hub.jncc.gov.uk/assets/478f7160-967b-4366-acdf-8941fd33850b). These documents may not be accessible to assistive technology.

The developer must comply with the legal protection of freshwater pearl mussels.

The developer may need a wildlife licence (https://www.gov.uk/government/publications/protected-species-apply-for-a-mitigation-licence-a05-and-a05a) to carry out their proposed activity.

When to ask for a survey

You should ask for a survey if either of the following apply:
- historical or distribution records show that freshwater pearl mussels may be present – you can search the National Biodiversity Network Atlas (https://nbnatlas.org/) by species and location
- the development proposal affects clean, fast-flowing rivers across northern England, Shropshire or Devon - the habitat for freshwater pearl mussels
Absence of a record does not mean there are no freshwater pearl mussels. It could mean there is no survey data available for that location.

You must check if the ecologist is qualified and experienced to carry out surveys for freshwater pearl mussels. CIEEM publishes advice on the valid age of ecological reports and surveys (https://cieem.net/wp-content/uploads/2019/04/Advice-Note.pdf).

Assess the effect of development on freshwater pearl mussels

Developers should submit information with their planning application on how their development proposal avoids or mitigates harm to freshwater pearl mussels.

Freshwater pearl mussels are sensitive to pollution and depend on salmon and trout. Development proposals that affect either of these will harm the species.

Harmful activities include:
- disturbing the mussel beds
- intensive land-use near water courses
- river engineering or works, such as dredging river shingle, sand and gravel
- storing materials in the water
- using machinery and vehicles in the water
- removing (abstracting) water and changing river flow
Activities may also be harmful if they:
- reduce water quality, for example, discharged chemicals or nutrients that lower oxygen levels
- lead to a decline in populations of salmon or trout (the mussels’ host fish)
- lead to a decline in habitat conditions, such as loss of tree cover that provide shade for mussels
- pollute the water or cause silt and sediment deposits (siltation)
Avoidance, mitigation and compensation measures

Where possible development proposals should avoid negative effects on freshwater pearl mussels. Where this is not possible, the developer will need to include adequate mitigation or, as a last resort, compensation measures in their development proposal to allow you to make a planning decision.

To avoid possible negative effects on freshwater pearl mussels, developers could redesign the development proposal to:
- avoid disturbing the river bed
- alter the timing of works, doing work outside of sensitive periods
- change the methods of working
Where this is not possible, mitigation should include how the developer will:
- protect the species population and distribution
- protect the river bed and the habitat immediately around it
- consider how other species, such as the mussels’ host fish could be affected by the mitigation
Mitigation measures can include:
- doing work in small sections
- reducing disturbance to the river bank
- reducing the area affected
- preventing any sediment from being released into the water
- preventing water pollution including silt
If the development proposal cannot mitigate for harm, then compensation measures must be in place to:
- improve the size and quality of the mussels’ habitat
- fix any broken connections to the mussels’ habitat
Compensation measures can include:
- supporting captive breeding and reintroduction programmes
- providing habitats to replace any that will be lost
- improving the quality of existing habitats
The developer can improve existing habitats if they:
- reduce the effect of sediment upstream of the mussel beds by fencing off river banks, creating buffer zones or shoring up (supporting) banks by managing or planting new trees
- stop nutrients and sediment from entering the river from sources of pollution such as ditches, cattle drinking points, roads and farms
- control non-native and invasive plant species
- carry out in-channel works to maintain water flow and improve river bed composition by removing weirs or other structures
- improve the survival of fry and juvenile mussels by cleaning and adding river gravel or boulders
- install large woody debris to improve habitat conditions for host fish
For more information on mitigation plans and compensation measures, read Protected species and development: advice for local planning authorities (https://www.gov.uk/guidance/protected-species-how-to-review-planning-applications#agree-avoidance-mitigation-or-compensation-measures).

Planning and licence conditions

The developer may need to apply for a freshwater pearl mussel mitigation licence (https://www.gov.uk/government/publications/protected-species-apply-for-a-mitigation-licence-a05-and-a05a) if their activities are likely to affect freshwater pearl mussels. You may also need to add mitigation or compensation strategies as a condition of planning permission.

Before you can grant planning permission, you must:
- work with the relevant ecologist to make sure these conditions do not conflict with the requirements of a freshwater pearl mussel licence
- be confident that Natural England will grant a wildlife licence – read section 4 of Protected species and development: advice for local planning authorities (https://www.gov.uk/guidance/protected-species-how-to-review-planning-applications)
For freshwater pearl mussels, Natural England will only issue a licence if the development proposal enhances the species’ habitats and helps to conserve them.

You do not need to consult Natural England on the wording or discharge (approval) of any conditions you impose on a development proposal. Natural England is unable to provide advice on this.

Natural England will not generally issue a licence until planning conditions relating to protected species have been discharged. This applies to conditions that are intended to be and capable of being discharged before development begins.

Natural England will only confirm if you need a licence when the development proposal is a Nationally Significant Infrastructure Project (NSIP).

Enhance biodiversity

To meet your biodiversity duty (https://www.gov.uk/guidance/biodiversity-duty-public-authority-duty-to-have-regard-to-conserving-biodiversity), you should suggest ways for the developer to:
- create new or enhanced habitats on the development site
- achieve improvements in biodiversity through good design
- follow other relevant plans and strategy for nature
Site management and monitoring

You should consider the need for site monitoring and management. These measures are likely to be needed by protected species licences.

A site management and monitoring plan should make sure:
- water quality is good
- water flow is maintained
- populations remain healthy
- water bodies are free from non-native species
- there’s no interference to habitat after development
- gravel bed habitat and woody debris is maintained
This can include additional survey work to check that mitigation measures are working as intended, followed by remedial work if needed.