The 473ha Slimbridge site is situated on the shore of the Severn Estuary almost midway between Gloucester and Bristol. The reserve is 270 ha and forms part of the Upper Severn Estuary SSSI, SPA and Ramsar site. WWT manage 210ha which are within the protected areas, including 55ha of saltings and saltmarsh pasture, and 8ha of foreshore above mean spring tide.
The Atlantic salt pasture is found on the seaward side of the sea wall, in an area known as “The Dumbles”. This is an EC Directive priority habitat. Important plant species are reflex saltmarsh grass, poa-like saltmarsh grass, bulbous foxtail and sea milkwort.
The majority of the site is the reclaimed pasture between the River Severn and the Gloucester to Sharpness Canal. Formerly managed primarily for wintering geese, the reserve now has a mosaic of goose pasture and seasonally flooded grasslands, which attract a wider range of wintering and breeding waterbirds. In addition there are reedbeds, open water lagoons, ditches and pools.
The reserve was designated for nationally important numbers of European white-fronted goose, Bewick’s swan, gadwall, teal, pintail, pochard, and wigeon amongst others. The birds feed on the habitat mosaic of shallow water and short grass sward produced by grazing cattle and control of water levels. Lapwing, oystercatcher and redshank all breed on the wet grassland. The site is regularly visited by Biodiversity Action Plan species - otter and polecat - and water voles are present in good numbers across the reserve area.
The nationally rare plant grass-poly (listed in both the British Red Data Book and on Schedule 8 of the Wildlife and Countryside Act) grows in the Rushy and Big Pen. While regionally important flora includes the unusual wasp orchid, sea arrowgrass, and mistletoe.