Marazion Marsh
| Site of Special Scientific Interest | |
 Location within Cornwall
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| Coordinates | 50°07′31″N 5°28′33″W / 50.1253°N 5.4758°WCoordinates: 50°07′31″N 5°28′33″W / 50.1253°N 5.4758°W |
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| Interest | Biological |
| Area | 63.3 hectares (0.6330 km2; 0.2444 sq mi) |
| Notification | 1951 |
Marazion Marsh is a Royal Society for the Protection of Birds (RSPB) reserve situated in a shallow river valley, half a kilometre to the west of Marazion, Cornwall, UK. It is separated from the coast by a shingle bar and small sand dune system and contains Cornwall’s largest reed bed.
Marazion Marsh lies to the west of the town of Marazion and 3.5 kilometres (2.2 mi) east of Penzance. The marsh is in an embayed estuary and is separated from Mount's Bay by a fossilised sand and gravel barrier which (except in extreme weather conditions) prevents access to the marsh by the sea. A discontinuous and eroded sand dune system is crossed by the main Penzance to Marazion road (formally the A394). The recent deposits sit on Lower Devonian Mylor Slates. The Red River (also known as the Marazion River) drains the Phragmites dominated marsh.
The most significant threat to the marsh at present is the runoff of soil particles in the area near the wetland. Because of this, the marsh's catchment is recognized as a Catchment Sensitive Farming Area, and the UK government works with farmers in the area to help control erosion.
A series of boreholes have been drilled into the marsh which found up to 10 metres (33 ft) of unconsolidated sedimentary material over weathered bedrock. Material from the Holocene was found. From these deposits paleoenvironmental information can be examined which include particle sizes, stratigraphy, pollen and diatoms. Evidence from the pollen was used to reconstruct the type of vegetation in the lower organic-rich horizons and samples sent to the Godwin Laboratory, University of Cambridge, for radiocarbon dating. The differing diatom flora show the changes in salinity through time. These deposits enable the reconstruction of the past environment of Marazion Marsh.
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