The Severn Estuary runs the length of Avon's coastal boundary, and is an internationally important wildlife habitat. This is reflected in its many designations: Site of Special Scientific Interest; Special Protection Area (under the EU Directive for Conservation of Wild Birds 1992); Natura 2000 site (under the EU Habitats and Species Directive 1992) and Ramsar site (under the Convention on Wetlands of International Importance). It is also being considered for designation as a Special Area of Conservation under the EC Habitats and Species Directive.

The estuary forms one of the most important inter-tidal zones in Britain, supporting a wide variety of habitats. As well as providing feeding grounds for over-wintering and migratory waders and wildfowl (such as dunlin, redshank and ringed plover), it also attracts a variety of migratory fish species (eg salmon, sea trout and twaite), and accommodates a number of rare plants (eg sea clover, sea barley and slender hare's-ear). It is however a fragile environment; its high tidal range carries the risk of flooding and erosion, and there are other threats from development, pollution and dredging for aggregates. To address these issues, local authorities and other organisations on both sides of the estuary (including local wildlife trusts) are preparing an Estuary Management Plan.