It is a 5,538 hectare biological Site of Special Scientific Interest (SSSI).

[5][7] Tollesbury Wick and part of Abbotts Hall Farm, both nature reserve managed by the Essex Wildlife Trust, are in the SSSI.

[3][8][9] Oysters have been harvested from the estuary for more than a thousand years and there are remains of fish weirs from the Anglo-Saxon era.

At the head of the estuary is the town of Maldon, which is a centre of salt production.

Within the estuary is Northey Island which was the location for the first experiments in the UK in 'managed retreat', i.e. creating saltmarsh by setting sea walls back from what are perceived to be unsustainable positions.