Introduction
The Wash NNR is the largest National Nature Reserve in England at 8800ha. Much of this is intertidal mud with a significant amount of saltmarsh bounded by high sea defence bunds which protect the intensively farmed hinterland from flooding. Two of the four main rivers that flow into the Wash, the Great Ouse and the River Nene both flow into the reserve.
The reserve, as part of the larger Wash SSSI, is internationally important for wintering waders and wildfowl and is the most important intertidal areas in the UK for birds.
There are two experimental bunds within the NNR, one of which is an important gull colony.
Habitats
The Wash is composed of tidal rivers, estuaries, lagoons, mud and sand flats and in the centre, deep channels surrounded by shallower waters. These areas predominantly consist of saltmarsh, intertidal banks of sand and mud, sandy and shingle beaches and subtidal sandy sediments.
The large areas of intertidal sand and mudflats form important habitat for polycheate worms, bivalves and crustaceans and foraging ground for wading bird species. Mussel and cockle beds found on the intertidal flats also support important fisheries in the area.
The extensive saltmarshes provide high tide roosting areas and low tide feeding areas for wildfowl and waders as well as nesting sites for some species such as redshank.
Mudflats
Intertidal mud and sand flats support a variety of polychaete worms and bivalve molluscs including cockle and mussel beds which alongside algae provide rich foraging grounds for a number of bird species. These include the dark-bellied brent goose, oystercatcher, common scoter, sanderling, gadwall, curlew, pintail, shelduck, dunlin, knot, bar-tailed godwit and black-tailed godwit.
Sandbanks
The sand banks are important for harbour seals, providing key habitat for breeding and hauling-out.
Saltmarsh
Further inland saltmarsh provides important roosting habitat at the site for a number of bird species, including redshank, curlew, pintail and dunlin. Saltmarsh also provides an important foraging habitat for the dark-bellied brent goose, wigeon, pintail and dunlin and is an important breeding area for redshank.
Shallow coastal waters and tidal rivers
Shallow coastal waters provide a nursery ground for commercially fished species of fish which are also food for tern species.
Sabellaria reef
The site has an outstanding example of the habitat Sabellaria spinulosa reef which in turn supports a wide variety of marine species.
Key species
Wintering wildfowl
The whole site supports a peak count of over 350,000 non-breeding waterbirds, including internationally important numbers of 17 species making it the most important intertidal site in the country.
The wildfowl include: dark-bellied brent goose, pink footed goose, wigeon, gadwall, pintail, shelduck and teal.
Wintering waders
Huge numbers of wading birds spend the winter in the Wash feeding upon the shellfish and worms. These include: oystercatcher, sanderling, curlew, dunlin, knot, grey and golden plover, bar-tailed godwit and black-tailed godwit.
Breeding birds
Redshank are the key breeding bird to be found on the saltmarshes of the Wash. With the Wash providing 10% of the UK’s saltmarsh habitat the population of breeding redshank is nationally important.
Harbour seals
The Wash is home to the largest colony of harbour seals in the UK, around 7% of the UK breeding population, and they can be found hauling out on sand and mudflats throughout the NNR.
Marine life
The sand banks and mudflats of the Wash are full of marine life from bivalves like the cockles that are commercially harvested to dense beds of brittlestars. The vast areas of intertidal mud provide the perfect conditions for marine worms, which attact many of the long-billed wading birds.
The shallow waters of the Wash are an important nursery area for several species of fish including, plaice, sole, cod and whiting.
Further info
Natural England’s West Midland NNRs:
Blog post: https://englandsnationalnaturereserves.co.uk/2026/03/25/revisiting-the-wash/
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