The Mersey Estuary although being highly developed, shows extensive areas of intertidal Sand and mud flats and reclaimed marshland.To the landward side of The Runcorn/ Widnes  bridge there are still maintained some undeveloped high salt marsh and brackish marshes .
The Estuary is of considerable importance for Wildfowl and Waders, with an average winter maximum wildfowl count of 28,800 and of waders 33,699. Of specific importance are  Dunlin (calidris alpina) Redshank (Tringa totanus) Shelduck (Tandorna tandorna) Teal (Anas crecca) Pintail   (A.acuta)
Of which  the Mersey winters 15% of the European winter population. There are also Wigeon, Pochard, Tufted, Shovelor, Gadwell, Goldeneye, Pinkfoot geese Grey lag geese, Canada geese, Whitefront geese, Golden plover, Snipe and woodcock.