Area: 59.9 hectares.
Marazion Marsh is situated at the head of Mounts Bay approximately 0.5 km west of Marazion and 5 km east of Penzance. The site extends over the floor of a wide, level coastal valley and is separated from the coast by a shingle bar and a narrow belt of sand dunes.
Marazion Marsh is underlain by Mylor beds of Lower Devonian age. These are mainly overlain by extensive alluvial deposits and peat, although valley gravels outcrop on the higher ground to the west. The resultant soils are acidic alluvial gleys.
The most extensive habitat types are the dense willow carr and reed-marsh, Marazion Marsh being the largest area of reed-marsh in Cornwall. Other habitats include streams, open water, unimproved grassland and scrub.
Noteworthy plant species occurring here include the nationally rare wavy-leaved St John’s-wort Hypericum undulatum, yellow centaury Cicendia filiformis and pillwort Pilularia globulifera.
The large areas of common reed Phragmites australis form the most westerly reedbed on the English mainland. Marazion Marsh is therefore of particular importance for its bird life especially as it provides a strategic feeding ground for passage waders. The site also supports the most westerly Acrocephalus warbler colony in England, with over 50 species of breeding sedge/reed warblers having been recorded here, plus a breeding pair of the nationally scarce Cetti’s warbler Cettia cetti. In addition yellow wagtail Motacilla flava and quail Coturnix coturnix both rare breeders in Cornwall, are known to breed here.
The site also supports large numbers of wintering passage birds, including a population of over 100 wintering teal Anas crecca. Some of the rarer wintering birds include bittern Botaurus stellaris and little stint Calidris minuta. Other rare passage birds recorded here include osprey Pandion haliaetus, nightingale Luscinia megarhynchos and red-breasted flycatcher Ficedula parva.
A total of 39 species of breeding birds, 76 species of passage birds and 56 species of wintering birds have been recorded at Marazion.
Marazion Marsh is also important for its high number of dragonfly species. Some 14 species have been recorded and of particular note is the Red Data Book species, the scarce chaser Libellula fulva. The two nationally scarce spices, the common hawker Aeshna juncea and the keeled skimmer Orthetrum coerulescens also occur.