The Mersey Estuary is an internationally important site for wildfowl and consists of large areas of intertidal sand and mudflats.
The site also includes an area of reclaimed marshland, salt-marshes, brackish marshes and boulder clay cliffs with freshwater seepages.
The Manchester Ship Canal forms part of the southern boundary of the site and separates a series of pools from the main estuary. These pools together with the Hale Marsh are important roosting sites for wildfowl and waders at high tide.
Throughout the winter the estuary supports large numbers of wildfowl and waders. The birds feed on the rich invertebrate fauna of the intertidal sediments as well as plants and seeds from the salt-marsh and adjacent agricultural land.
The estuary is also a valuable staging post for migrating birds in spring and autumn.
In 1980-81 the estuary had the highest monthly count of wildfowl of any British site; 57,000 birds. The most important species over the period 1978-83 were Pintail (Anas acuta) (17% of the total W European population), Teal (Anas crecca) (12%), Shelduck (Tadorna tadorna) (7%) and Wigeon (Anas penelope) (2%). In 1982-83 the estuary had the 16th highest monthly count of waders on any British site; 26,593 birds.
The most important species over the period 1978-83 was Dunlin (Calidris alpina) (1%). However, nationally important numbers of Curlew (Numenius arquata), Redshank (Tringa totanus) and Golden Plover (Pluvialis apricaria) were also recorded.
Several areas of salt-marsh are present. These form important feeding and roosting sites for birds. Glasswort (Salicornia spp.) is widespread on the outer margins whilst Common Saltmarsh Grass (Puccinellia maritima) is dominant over the rest. Unlike the other salt-marshes in the estuary, Stanlow banks has not been grazed by sheep or cattle and consequently has a more diverse flora. Sea Aster (Aster tripolium) and Hastate Orache (Atriplex prostata) are widespread throughout this area. Sea Plantain (Plantago maritima), Annual Seablite (Sueda maritima) and Scurvey-grass (Cochlearia spp.) also occur.
In a number of areas the salt-marsh grades into brackish marsh dominated by Common Reed (Phragmites australis) with Sea Arrow-grass (Triglochin maritima) and Great Reedmace (Typha latifolia) also present in some areas. On the sandy foreshores Sea Sandwort (Honkenya peploides) also occurs with Sea Milkwort (Glaux maritima). At the inner edge of the salt-marsh and along the strand-line, Mud Rush (Juncus gerardi), Sd Sedge (Carex arenaria) and Curled Dock (Rumex crispus) occur.
On the north side of the estuary, part of the coastline is formed by boulder clay cliffs. Portions of the cliff have become exposed by slumping and in these areas a number of unusual species occur including Yellow-wort (Blackstonia perfoliata) and Bristly Oxtongue (Picris echioides) both of which are at the northern limits of their distribution.
English Nature citation details:
File Ref: C/S/13
Site Name: Mersey Estuary
District: Ellesmere Port/Vale Royal/Halton/Wirral/Liverpool
Status: Site of Special Scientific Interest (SSSI) notified under Section 28 of the Wildlife and Countryside Act 1981.
Local Planning Authority: Cheshire County/Merseyside Metropolitan County Councils
National Grid Reference: SJ 440 800
Area: 6702.14 ha. 16561 ac.
Ordnance Survey Sheet 1:50,000: 108, 117
Date Notified (under 1949 act): 1951 Date of last revision: 1979
Date Notified (under 1981 act): 1984
l. Hale Duck Decoy is a sheduled ancient monument and is managed as a reserve by the Cheshire Wildlife Trust.
2. Boundary modified at renotification by extensions and deletions.