Area: 279.2 hectares.
Description and Reasons for Notification:
St. John’s Lake lies immediately south of Torpoint and forms part of the Tamar-Lynher estuarine system. At low tide, extensive mud flats are exposed providing important feeding grounds for large populations of wintering wildfowl and waders. The lake has interesting areas of species-rich saltmarsh, and the underlying Devonian slates form fringing shingle beaches and shallow rock cliffs supporting stunted trees and scrub. Although much of the site is bare mud, there are considerable areas covered with the green alga Enteromorpha and beds of the rare narrow leaved eel grass Zostera angustifolia and the locally distributed dwarf eel grass Z. noltii.
The saltmarsh habitats are not extensive and consist predominantly of common cord-grass Spartina anglica. There is however a strong population of sea purslane Atriplex portulacoides, a species which is uncommon in Cornwall. In addition there is a small upper salt marsh community supporting common salt marsh-grass Puccinellia maritima with sea plantain Plantago maritima, sea milkwort Glaux maritima and saltmarsh rush Juncus gerardi.
St. John’s Lake is of national importance for its wintering population of around 6,000 wildfowl and 10,000 waders. The alga and eel grass beds are particularly important as they provide feeding areas for a large population of up to 5,000 wigeon Anas penelope. Mute swan Cygnus olor, Brent geese Branta bernicla, shelduck Tadorna tadorna and teal Anascrecca all occur in high numbers. The soft mud flats attract a nationally important population of black tailed godwit Limosa limosa, which are regularly present in winter in numbers up to 150, 3–4% of the British wintering population. The mud flats are an important feeding ground for some 3,000 dunlin Calidris alpina, 600 knot C. canutus, 300 oystercatchers Haematopus ostralegus, 200 curlew Numenius arquata and 600 redshank Tringa totanus. Turnstone Arenaria interpres, spotted redshank Tringa erythropus, grey plover Pluvialis squatarola and ringed plover Charadrius hiaticula also frequent the site. In addition, there is a very large gull roost containing up to 14,000 black-headed gulls Larus ridibundus.