2018 Natural England (NE) Digital video aerial surveys of red-throated diver in the Outer Thames Estuary Special Protection Area dataset https://portal.medin.org.uk/portal/start.php?tpc=010_21a79c3c1de95de1a93456d3c9885a13 This report provides a new population estimate for the original Outer Thames Estuary SPA for red throated diver of 21,997. The estimated total for the new, enlarged SPA (formerly the pSPA) is 22,280. Both these figures are approximately 3.5 times greater than the notified population of the original SPA (6,466 individuals). This increase in the recorded number of red-throated divers, coupled with the numbers of individuals of other species recorded has resulted in a peak waterbird population estimate across the original SPA of 41,918 and across the newly enlarged SPA of 46,056 individuals. This suggests that on occasion the SPA supports an assemblage of wintering waterbirds well in excess of the size (20,000 individuals) required to consider this to be qualifying feature of the SPA. Red-throated divers appear to use the additional area now included within the larger revised SPA boundary at low densities and at high tide when mudflats are covered. Anthropogenic effects on the distribution of several species were detected, notably strong displacement of red-throated diver was noted from areas within offshore windfarms and from areas of shipping activity. This lead to higher densities of birds at points furthest from anthropogenic activity. 20180628