The marshes are one of 22 environmentally sensitive areas recognised by the UK's Department for Environment, Food and Rural Affairs (DEFRA).
Steeper gravel beaches with hills behind and segments of low cliff in the east at Whitstable and Herne Bay form the most notable exceptions, along a stretch of about 4 miles (6.4 km).
The marshes have been recognised as one of the most important natural wetlands in northern Europe, and they are monitored by local landowners and wildlife custodians.
[4] According to the RSPB, up to 300,000 migrant birds use the mudflats of the Thames marshes as a haven each year in their migratory journeys between the Arctic and Africa.
They maintain reserves at Cliffe pools, Northward hill, High Halstow and Elmley Marshes, Sheppey.