The Devon Avon Estuary MCZ covers an area of 2 km2 and is located on the south coast of Devon, in the Western Channel and Celtic Sea region. The site extends from the mouth of the estuary up to a tidal weir at Aveton Gifford.
The Devon Avon Estuary is a narrow meandering drowned river valley of about 7 km in length, which lies within a steep sided valley. It is characterised by a subtidal river channel bisecting the intertidal areas, which are sandy in the outer reaches and muddier in the inner reaches. The mouth of the estuary has semi-exposed rock platforms with rich rockpool, under-boulder and overhang communities on the lower shore.
The Devon Avon Estuary MCZ is an important site supporting a variety of habitats and wildlife. Various species of worm, crustacean and shrimp can be found here, including the nationally scarce tentacled lagoon worm. This is a tiny bristleworm which grows up to 5 mm in length. It creates and lives in tubes within the mud habitats of the estuary. These worms have tentacles around their mouths used for gathering food from the surrounding muddy sediments. The tentacled lagoon-worm is particularly vulnerable to activities that cause changes in its habitat.
Like all of the main estuaries of the south west, the Devon Avon Estuary is an important nursery area for fish species and is potentially important for seahorse populations as it provides suitable food and shelter. The saltmarshes provide habitat for crustaceans (such as crabs, lobsters and barnacles), molluscs (such as mussels and oysters) and a nursery area for fish, as well as feeding grounds for birds.