The Wash is one of Europe’ s most important estuaries for birds as defined by its status as an Special Protection Area (SPA) and, in combination with the Norfolk Norfolk Coast as a Special Area of Conservation (SAC). The SAC covers ~1,078 km2 with the SPA covering around 622 km2 (c. 58% of the cSAC) broadly situated landward of a line from Gibraltar Point in Lincolnshire to Holme in North Norfolk). This is often referred to as the ‘Inner’ Wash in this document to prevent confusion with the Greater Wash Strategic Area earmarked for windfarm development. A large tidal range (6m average on spring tide) creates a large proportion of inter-tidal waters especially in the south near the mouths of the rivers Great Ouse and Nene and along the along the eastern and western flanks of the Norfolk and Lincolnshire coast respectively. The Wash forms the largest embayment in the UK and some 51% of the cSAC is thus classed as ‘sea inlet’ incorporating habitats such as tidal rivers, estuaries, mud flats and sand flats. An important habitat division is the sandbanks, which are slightly covered by water at all times (subtidal) and the mudflats and sandflats, which are exposed at low tide (intertidal). The Wash supports the second largest area of intertidal flat in the UK, which is of enormous significance to a wide range of species, especially waders and waterfowl (ducks, geese and swans), particularly in winter and on passage. The site designation reports that 400,273 individual waterfowl (5 year peak mean from 1991/2-1995/6) regularly use the area in winter. This is some 20-fold higher than the 20,000 waterfowl required for the area to meet the EC assemblage qualification as a wetland of international significance. The primary objective of the boat-based surveys of the Wash documented here was to broadly establish the summer distribution, abundance (population size and density) and activity of birds, especially breeding terns (Sandwich Sterna sandvicensis and Common terns Sterna hirundo) in relation to the proposed cable route corridor of the proposed Lincs offshore wind farm. This extends over about 40 km in total from the wind farm to the landfall point, located to the east of the mouth of the River Nene . The surveys also formed part of a wider survey programme to determine the relative use of the Wash by breeding terns, particularly Sandwich Terns, from the colonies at Scolt Head and Blakeney Point.