Research and analysis

Waterbody prioritisation for native oyster (Ostrea edulis) restoration in England: summary

Published 27 October 2026

Applies to England

1. Chief Scientist’s Group report summary

This report presents a national-scale assessment of the feasibility and prioritisation of restoring European native oyster (Ostrea edulis) reef habitats across English coastal and estuarine waterbodies. Using a structured, evidence-based approach, the study identified locations where ecosystem-scale restoration is most feasible and likely to deliver significant environmental and socio-economic benefits.

1.1 Background

Native oyster reef restoration is a component of the Environment Improvement Plan (2025), which commits to restoring functional oyster reef habitat across 5 to 8 English waterbodies. To support this objective, the assessment considered 109 Water Framework Directive waterbodies with historical or contemporary evidence of native oyster presence. The aim was to identify waterbodies with suitable environmental conditions and prioritise those offering the greatest restoration potential at an ecosystem scale.

1.2 Approach

The assessment was completed in three stages. First, waterbodies were assessed for evidence of historical or recent presence of native oyster. Second, waterbodies were screened against environmental criteria including salinity, dissolved oxygen, temperature, suspended sediment levels, and the availability of sufficient restoration area. The third stage prioritised suitable sites using a multi-criteria framework that considered environmental management objectives, socio-economic benefits, opportunities for interaction with other habitats, and potential risks such as disease and competing marine activities. Sensitivity testing was undertaken to assess the effect of varying key prioritisation factors.

1.3 Results

Of the 109 waterbodies assessed, 49 were identified as potentially suitable for restoring functional native oyster reef habitat. Of these, 38 were considered capable of supporting restoration at an ecosystem scale and progressed to the prioritisation stage.

The assessment identified sixteen highest-priority waterbodies: Mersey Mouth, Wash Inner, Wash Outer, Solent, Blackwater, Blackwater Outer, Medway, Portsmouth Harbour, Thames Lower, Cumbria, Tyne and Wear, Helford, Langstone Harbour, Chichester Harbour, Beaulieu River and Plymouth Tamar.

Sensitivity testing demonstrated that eleven of these sites consistently remained within the highest-priority category when key weighting factors were removed. These included Mersey Mouth, Wash Inner and Outer, Solent, Blackwater and Blackwater Outer, Medway, Portsmouth Harbour, Thames Lower, Chichester Harbour, and Beaulieu River. These waterbodies represent the strongest candidates for contributing to national restoration targets.

1.4 Conclusions

This assessment provides an important first step in identifying priority waterbodies for ecosystem-scale native oyster reef restoration in England. It establishes a national evidence base to support delivery of the Environment Improvement Plan commitment and provides a consistent basis to help focus further assessment and prioritisation.

The assessment was constrained by the availability of national-scale datasets. Factors including additional marine uses, pH and the abundance of invasive non-native species could not be fully incorporated and should be considered in subsequent assessments. Uncertainties also remain around the effects of climate change and ocean acidification, including altered hydrodynamics, larval retention and marine heatwaves, which may influence long-term restoration success.

The outputs should therefore be used as a strategic prioritisation rather than as confirmation that individual sites are suitable for restoration. For example, they could help inform the prioritisation of restoration opportunities within catchments through River Basin Management Plans. Further assessment of priority waterbodies will be needed to consider local environmental conditions, pressures, constraints and delivery opportunities before restoration sites are identified. In this way, the assessment provides a starting point for moving from national-scale prioritisation towards the identification and development of viable restoration opportunities.

The findings will inform further prioritisation and evidence-gap work led by the Environment Agency through Restoring Meadows, Marsh and Reef (ReMeMaRe), with Defra group partners, helping to identify future restoration opportunities and inform marine policy and planning.

1.5 Publication details

This summary relates to information from the following project:

• Title: Waterbody prioritisation report for Native Oyster (Ostrea edulis) restoration in England
• Science manager: Hannah Westoby, Estuaries and Coasts team
• Research Contractor: Anna Cucknell, Zoological Society of London (ZSL)

This project was commissioned by the Environment Agency’s Coasts and Estuaries team and published by the Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

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