The river is important for its dragonfly communities, with a strong population of Scarce Chaser (found in only six other areas in England), together with a strong population of White-legged Damselfly.
Red-eyed Damselfly is also found.
The river is also important for aquatic plants, including Loddon Pondweed.

The Kellaways – West Tytherton Site of Special Scientific Interest, 3 miles (4.8 km) north east of Chippenham, is of geological interest as the river bank exposes Callovian highly-fossiliferous sandstone which contains well-preserved bivalves, gastropods, brachiopods, belemnites and ammonites.
Further downstream at Newton St Loe the Newton St Loe SSSI is another Geological Conservation Review SSSI.
It represents the only remaining known exposure of fossiliferous Pleistocene gravels along the River Avon.
In conjunction with other sites within the wider area, it has aided the development of a scientific understanding of the history of early glaciation within South West England.
The bodies of mammoths (Mammuthus) and horses (Equus) have been found at the site.

The Avon Gorge has been designated as a Site of Special Scientific Interest because it supports some rare fauna and flora, including species unique to the gorge.
There are a total of 24 rare plant species and two unique trees: the Bristol and Wilmotts's whitebeams.
Other notable plants include Bristol Rock-cress, Bristol onion, Spiked Speedwell, Autumn Squill and Honewort.
Other areas along the river which have this designation include Bickley Wood, Cleeve Wood, Hanham for its large population of Bath Asparagus (Ornithogalum pyrenaicum).
Stidham Farm near Keynsham contains at least At least 2 metres (7 ft) of Pleistocene terrace-gravels, consisting of limestone clasts mainly, but also with Millstone Grit, Pennant Sandstone, flint and chert clasts.
The site is of considerable importance for studies relating to the possible glaciation of the area, and of the terrace stratigraphy, particularly as it is one of only two accessible terrace deposits in this part of the Avon valley.
Newton St Loe SSSI is also listed for geological reasons as it represents the only remaining known exposure of fossiliferous Pleistocene gravels along the River Avon.
In conjunction with other sites within the wider area, they have aided the development of a scientific understanding of the history of early glaciation within South West England.

At Horseshoe Bend, Shirehampton the wooded cliff and a narrow salt marsh are supported by rocks of Devonian sandstone and Carboniferous limestone, overlain by with Triassic Dolomitic conglomerate.
The site's principal interest and the reason for its designation as an SSSI is the presence of a population of the True Service-tree (Sorbus domestica) growing on the cliffs.
This tree is nationally rare in Britain, and this site hosts the largest known population in England.
Other notable species of Sorbus here are the whitebeams Sorbus eminens and Sorbus anglica, both of which are also nationally rare in Britain.
The nationally scarce Large-leaved Lime (Tilia platyphyllos) also occurs, and herbs include Field garlic (Allium oleraceum) and Pale St. John's-wort (Hypericum montanum).
The saltmarsh vegetation, which lies at the base of the cliff, is predominantly made up of Sea Aster (Aster tripolium) and English Scurvygrass (Cochlearia anglica).
There are however two nationally scarce vascular plant species here as well – Slender Hare's-ear (Bupleurum tenuissimum) and Long-stalked Orache (Atriplex longipes).

The tidal reaches of the River Avon provide habitat for waterbirds, with 64 species having been recorded up to 2004, including 21 species of shorebird, and 13 species of gull.
The river is important for its dragonfly communities, with a strong population of Scarce Chaser (found in only six other areas in England), together with a strong population of White-legged Damselfly. Red-eyed Damselfly is also found. The river is also important for aquatic plants, including Loddon Pondweed.
The Kellaways – West Tytherton Site of Special Scientific Interest, 3 miles (4.8 km) north east of Chippenham, is of geological interest as the river bank exposes Callovian highly-fossiliferous sandstone which contains well-preserved bivalves, gastropods, brachiopods, belemnites and ammonites. Further downstream at Newton St Loe the Newton St Loe SSSI is another Geological Conservation Review SSSI. It represents the only remaining known exposure of fossiliferous Pleistocene gravels along the River Avon. In conjunction with other sites within the wider area, it has aided the development of a scientific understanding of the history of early glaciation within South West England. The bodies of mammoths (Mammuthus) and horses (Equus) have been found at the site.
The Avon Gorge has been designated as a Site of Special Scientific Interest because it supports some rare fauna and flora, including species unique to the gorge. There are a total of 24 rare plant species and two unique trees: the Bristol and Wilmotts's whitebeams. Other notable plants include Bristol Rock-cress, Bristol onion, Spiked Speedwell, Autumn Squill and Honewort. Other areas along the river which have this designation include Bickley Wood, Cleeve Wood, Hanham for its large population of Bath Asparagus (Ornithogalum pyrenaicum). Stidham Farm near Keynsham contains at least At least 2 metres (7 ft) of Pleistocene terrace-gravels, consisting of limestone clasts mainly, but also with Millstone Grit, Pennant Sandstone, flint and chert clasts. The site is of considerable importance for studies relating to the possible glaciation of the area, and of the terrace stratigraphy, particularly as it is one of only two accessible terrace deposits in this part of the Avon valley. Newton St Loe SSSI is also listed for geological reasons as it represents the only remaining known exposure of fossiliferous Pleistocene gravels along the River Avon. In conjunction with other sites within the wider area, they have aided the development of a scientific understanding of the history of early glaciation within South West England.
At Horseshoe Bend, Shirehampton the wooded cliff and a narrow salt marsh are supported by rocks of Devonian sandstone and Carboniferous limestone, overlain by with Triassic Dolomitic conglomerate. The site's principal interest and the reason for its designation as an SSSI is the presence of a population of the True Service-tree (Sorbus domestica) growing on the cliffs. This tree is nationally rare in Britain, and this site hosts the largest known population in England. Other notable species of Sorbus here are the whitebeams Sorbus eminens and Sorbus anglica, both of which are also nationally rare in Britain. The nationally scarce Large-leaved Lime (Tilia platyphyllos) also occurs, and herbs include Field garlic (Allium oleraceum) and Pale St. John's-wort (Hypericum montanum). The saltmarsh vegetation, which lies at the base of the cliff, is predominantly made up of Sea Aster (Aster tripolium) and English Scurvygrass (Cochlearia anglica). There are however two nationally scarce vascular plant species here as well – Slender Hare's-ear (Bupleurum tenuissimum) and Long-stalked Orache (Atriplex longipes).
The tidal reaches of the River Avon provide habitat for waterbirds, with 64 species having been recorded up to 2004, including 21 species of shorebird, and 13 species of gull.
River Avon, Bristol