Marine Biosecurity on the Stour and Orwell Rivers.
A Deep Dive into Protecting Vital Waterways
Introduction
Marine biosecurity refers to the strategies used to protect aquatic ecosystems from harmful organisms and substances that can be introduced through human activity. This includes invasive species, diseases, and contaminants that threaten the health of native plants, animals, habitats, and the broader environment. On the Stour and Orwell rivers, two interconnected estuarine systems in eastern England, marine biosecurity is vital to safeguard the environment that supports rich biodiversity, thriving fisheries, and local communities.
The River Stour (forming much of the border between Suffolk and Essex) and the River Orwell (flowing through Ipswich into the North Sea) host unique ecosystems. Their brackish waters support a mix of freshwater and marine species, making them particularly sensitive to biosecurity threats. Marine biosecurity here not only helps maintain ecological balance but also protects economic activities such as fishing, boating, and tourism.
Introduction to Marine Biosecurity
Marine biosecurity covers practices designed to prevent the introduction and spread of harmful organisms and diseases in aquatic environments. These threats can come from hull fouling on boats, ballast water discharge, contaminated equipment, or even deliberately released non-native species. Once established, invasive organisms can be difficult, costly, or impossible to eradicate.
For communities around the Stour and Orwell rivers, biosecurity ensures the health of important shellfish beds, fish populations, and habitats like salt marshes and mudflats, which are crucial for birds and other wildlife.
Overview of the Stour and Orwell Rivers
River Stour Ecosystem
The River Stour estuary is a mosaic of tidal channels, mudflats, saltmarsh, and reedbeds. This variety of habitats supports fish like flounder and sea trout, birds such as avocets and oystercatchers, and invertebrates like ragworms and lugworms that are important for both the food web and local bait fisheries.
River Orwell Ecosystem
Flowing past Ipswich before widening into an estuary, the River Orwell is characterised by brackish water that supports diverse life. It’s home to commercially and recreationally important fish (e.g., bass and mullet) and shellfish, plus waterbirds that rely on undisturbed feeding grounds.
Both rivers feed into the southern North Sea, meaning they are influenced by tidal patterns and marine species movements.
Common Biosecurity Threats in Marine and Estuarine Systems
Several types of threats can compromise the biosecurity of rivers like the Stour and Orwell:
Invasive Non-Native Species (INNS)
These are species introduced outside their normal range, often by shipping or movement of boats and gear. Examples found in UK estuaries include the American slipper limpet (Crepidula fornicata) and the pacific oyster (Crassostrea gigas). INNS can outcompete native species, alter habitats, and reduce biodiversity.
Disease and Pathogens
Diseases affecting shellfish and fish, such as Bonamia ostreae in oysters or viral hemorrhagic septicemia in fish, can devastate populations and impact commercial fisheries.
Human-Mediated Spread
Recreational boaters, anglers, aquaculture operations, and even kayaking can inadvertently transport organisms from one water body to another via wet equipment or contaminated bait.
Impacts of Biosecurity Breaches
Ecological Consequences
When invasive species take hold, they can change food webs, reduce native species, and transform habitats. For example, dense beds of non-native oysters can alter sediment dynamics, affecting mudflat invertebrates and the birds that feed on them.
Economic and Recreational Impacts
Local economies that depend on fishing, shellfish harvesting, tourism, and water sports can suffer if water quality declines or target species are lost. Biosecurity breakdowns can lead to costly management efforts and loss of income.
Current Biosecurity Measures on the Stour & Orwell
Local and National Regulations
The UK has regulations aimed at preventing the spread of INNS and diseases in waterways. Organisations like the Environment Agency and Natural England coordinate efforts, enforce controls, and issue guidance to stakeholders.
Monitoring and Surveillance Programs
Regular surveys help detect early signs of invasive species or disease outbreaks. Citizen science initiatives and professional monitoring both contribute valuable data.
Community and Stakeholder Engagement
Local boating clubs, anglers, environmental groups, and councils promote awareness and best practices. Education campaigns encourage behaviours that reduce risk.
Best Practices for Individuals and Organizations
Everyone has a role in protecting marine biosecurity:
Clean, Drain, Dry for Boats & Gear
Boats, trailers, fishing gear, and wetsuits should be cleaned thoroughly, drained of water, and dried between trips to different waterways.
Reporting Sightings and Incidents
If you see unusual species or signs of disease, report them to local authorities or through UK reporting services like the Non-Native Species Secretariat.
Supporting Restoration and Habitat Protection
Participate in or support local conservation projects that restore habitats such as salt marshes and reedbeds. These areas can resist invasion and boost resilience.
✓ Check and clean wetsuits, BCDs, regulators, weight belts, fins, masks, and gloves after use,
removing any plant or animal material. Use freshwater, paying close attention to niche areas
like seams, valves, and buckles where organic matter might get caught.
✓ Dry equipment and clothing before next use, ideally in a warm, ventilated space (e.g., a
designated dry room), for as long as possible.
✓ When visiting more than one area in a short period of time, use spare, dry clothing and
equipment between sites, if possible. If this is not possible, check and clean clothing and
equipment before leaving the area, as above, ensuring that any plant or animal material is
kept at that site and not moved to the next area.
Recreational watersports clubs
✓ Encourage members to take up biosecurity good practice and consider biosecurity when
undertaking sport with the club.
✓ Appoint a biosecurity champion to, for example, share information (see Raising Awareness
below), check biosecurity uptake and report INNS sightings.
✓ Include biosecurity and cleaning clauses and guidance in T&Cs for club membership. For
example:
Our Club expects members to:
1. Follow the principles of Check Clean Dry.
2. Take the initiative to improve their understanding of INNS and biosecurity (the Club will
signpost courses, training and interesting material where possible).
3. Promote and share awareness of INNS and biosecurity good practice between members.
4. Report any suspected INNS sightings by submitting records to iRecord.
5. Comply with all regulations and guidelines issued by the relevant authority.
✓ Understand the heightened risk posed by watersports events and consider what additional
biosecurity measures might be needed. Guidance for event biosecurity can be found on the
GB NNSS webpage and on the Paddle UK website.
Anglers
✓ Refrain from using live bait that has been caught outside of the local area. Refrain from using any bait that is known to be an INNS (e.g., American slipper limpet).
✓ If equipment is being used abroad, ensure that it is clean and dry before travelling out of
country and when re-entering country.
✓ Avoid discarding unwanted catch back into the ocean away from where it was caught. If you
pull up a known INNS, dispose of it appropriately on land if possible.
✓ Wash equipment into the same water body it has been in or wash down well away from the
water’s edge.
Case Studies and Success Stories
Local Initiatives
Projects involving community volunteers have helped monitor species along the Stour and Orwell, providing early detection and rapid response.
Lessons from Other Estuaries
Comparisons with other UK estuaries show the value of cooperation between ports, fishers, and regulators in reducing invasive species spread.
Challenges and Future Threats
Climate Change Effects on Estuaries
Warming waters and sea level rise may make conditions more favourable for some INNS, while stressing native species.
Balancing Development and Protection
Ports, marinas, and industrial activities need biosecurity planning to avoid unintended introductions.
Conclusion
Marine biosecurity on the Stour and Orwell rivers is essential for maintaining ecological balance, supporting local economies, and preserving recreational opportunities. By understanding threats, applying best practices, and working together, communities can protect these important waterways for generations to come.
Marine biosecurity means preventing harmful organisms and diseases from entering or spreading within aquatic environments, protecting ecosystems and human uses.
Their unique estuarine ecosystems support diverse wildlife, fisheries, and recreation, making them sensitive to invasive species and disease.
Through boats, fishing gear, ballast water, aquaculture activities, and movement of contaminated equipment.
Follow the “Clean, Drain, Dry” routine for all equipment between waterways.
Agencies like the Environment Agency, local councils, and volunteer groups conduct monitoring and raise awareness.
Yes — reporting helps authorities respond quickly and reduce impacts.
Article reproduced by kind permission of APEM Group published December 2025
