The site has varied habitats, such as saltmarsh, mud flats, shingle spits and former gravel pits. It is of international importance for wintering brent geese and black-tailed godwits, and of national importance for six other bird species, including little terns. It also has important assemblages of invertebrates and plants, such as golden samphire and shrubby seablite. A peat seam in St Osyph Marsh has been dated to 4280 BP, and this marsh is important for saltmarsh morphology.[2]
There are important geological exposures for Pleistocene studies at East Mersea; investigation is at an early stage, but they show warm climate deposits from one or more post-Anglianinterglacials.[2]
^ abcd"Colne Estuary citation"(PDF). Sites of Special Scientific Interest. Natural England. Archived from the original(PDF) on 8 December 2015. Retrieved 7 December 2015.
^"Map of Colne Estuary". Sites of Special Scientific Interest. Natural England. Retrieved 7 December 2015.