Shell Flat sandbank runs northeast from the southern corner of the site in a blunt crescent to the south west.The sandbank forms a continuous structure approximately 15km long from east to west. The bank is an example of a Banner Bank, which are generally only a few kilometres in length with an elongated pear/sickle-shaped form, located in water depths less than 20m below Chart Datum (CD). Shell Flat is considered to be an excellent example of Annex I sandbank Habitat. In terms of sediment type, the bank comprises a range of mud and sand sediments from silts and clays through to coarse sands. Shell Flat is characterised by its low biodiversity, high biomass and is noted as an important foraging ground for many over wintering bird species. Surveys have identified that a large population (50,000+) of the species feed on the submerged sandbanks. This has made the Liverpool Bay area the most important site in the UK for the sea duck.