Defending the Mersey Estuary

The future of the Mersey Estuary and its wildlife is at risk because of a proposal to build a concrete barrage across a narrow section of the estuary which will be used to generate electricity and it is also claimed will provide flood defence benefits.

The Mersey Estuary provides a multitude of services such as natural flood management, and carbon storage. Ensuring these services are maintained and enhanced will be crucial in not just helping tackle the nature and climate crises, but also supporting economic growth and thriving communities.  

Whilst details on the proposal remain limited, the fact that this proposal is being promoted is of serious concern given the severe damage that could occur to the estuary if it were constructed. We believe irreplaceable habitats, such as the intertidal mudflats, and saltmarshes could be lost or damaged if this project goes ahead. 

The 5,023 ha (50.23 km2) Mersey Estuary is the 10th best wetland in Britain for birds. It is the best place in the UK Shelduck and second-best for Dunlin and internationally important for 4 other species. 

The Mersey Estuary is located on the Irish Sea coast of north-west England. It is a large, sheltered estuary which comprises large areas of saltmarsh and extensive intertidal sand- and mud-flats, with limited areas of brackish marsh, rocky shoreline and boulder clay cliffs, within a rural and industrial environment. 

The Mersey Estuary supports over 100,000 non-breeding waterbirds, and is designated for – 

• Common shelduck  
• Dunlin  
• Black-tailed godwit  
• Common redshank  
• Eurasian teal  
• Northern pintail 
• European golden plover
• its Waterbird assemblage   

The Mersey Estuary also supports: 

• 1.2% of the UK’s saltmarsh (556.11 ha) 

• 1.6% of the UK’s mudflats (4,470 ha) 

• Important populations of European Eel; one of only two globally threatened species in the UK. 

• Recently recovered Atlantic Salmon populations, absent for almost a century before returning in 1999.  

• The RSPB has a 1,500ha reserve in the estuary, as well as 3 other coastal nature reserves. 

• The estuaries’ amazing habitats and species are recognised at an international level. As a result, it one of the most highly protected sites in the UK. It is designated as: 

• A Special Protection Area for its internationally important bird numbers, 

• a Ramsar site as an internationally important wetland,  

• and a Site of Special Scientific Interest for its nationally important habitats and wildlife. 

The Mersey Barrage proposal, if developed, would peobably represent one of the most environmentally damaging developments in the estuary and could pose a huge risk to the species and habitats which make this place so special. 

We are concerned that the way the Mersey Estuary which has the second highest tidal range in the UK and is connected to both the Irish Sea and inland river systems means that a barrage enclosing the estuary may increase two types of flooding:  

• Tidal flooding could occur in some areas through displacement of seawater, which could push more water onto adjacent coasts. This could also increase the erosion of natural flood defences.  

• River flooding could increase due to the barrage impeding the flow of the 69-mile long River Mersey, which is tidal from Howley Weir in Warrington, and the 71-mile long River Weaver which drains parts of Cheshire.  

A barrage will inevitably restrict water flow into the Irish Sea resulting in loss of sediment supply leading to erosion of intertidal areas, as has been seen in other barrage schemes elsewhere in the world. This may result in loss of the intertidal area, as well as the loss of carbon storage in the sediment. 

Water quality in the Mersey could also be severely impacted by the nutrients and sediment that would be trapped behind the barrage. This would present a very real risk of the estuary basin becoming a “green, fetid lake.”  

This is particularly worrying in relation to fish, for generations the Mersey was an industrial river, polluted almost to the point of death, but over 3 decades of tireless work by Mersey Rivers Trust and others have returned the river to health, this status is threatened by the proposal. 

Ultimately all these changes would alter and degrade the internationally important habitats of the Mersey Estuary and seriously damage the wildlife of this internationally important site. 

We will update the actions you can take to help as more information is made available. 

We are deeply sceptical that a barrage can be delivered without serious damage to the Mersey Estuary, and its wildlife. Experience from other barrage projects also suggests such a proposal is likely to have unacceptable costs to the public. 

We are in a climate and nature emergency – these two issues are inextricably linked. Climate change is one of the greatest threats to nature and people – we are seeing more extreme weather, destruction of habitats, and volatile food availability as temperatures change. Whilst we recognise the need for projects that reduce carbon emissions and manage future flood risk these must be done in a way that enhances the environmental and has positive social impacts. 

The reality of the Mersey barrage is that it would likely result in serious damage to the Mersey’s protected sites and their important habitats and species. There are likely impacts to not only the Mersey but the neighbouring Dee estuary and Sefton coast. This would be at odds with targets set out in the UK government’s 25-year environment plan.  

We consider sufficient evidence exists to demonstrate that a barrage is likely to be inappropriate on The Mersey and any proposed investment would be better invested on less environmentally damaging developments. 

Though we think it is unlikely the risks of the project can be mitigated, if the project progresses, we expect that the developer should engage constructively with environmental NGOs to try and minimise harm to nature. 

• Summer 2024- EIA scoping report expected Summer 

• February 2024- MTPP approached Planning Inspectorate for initial discussions 

• December 2023- Agreement between K-Water (operators of Siwa tidal power in S. Korea) and MTPP to share knowledge

• 2021-2024- Data gathering, survey, monitoring and modelling work overseen by Merseyside Environmental Advice Service (MEAS)