I pulled in to the Nature Reserve car park, and immediately spotted the bird, flying around, picking insects off the surface of the water, about 100m away. Every now and then the bird would settle on a small rock on the water, before being put up by a pair of Common Terns (year tick) and a couple of Black-headed Gulls. Here's a heavily cropped shot of the bird as it took off. The white wings and white tail and rump are very noticeable. I also managed to get some video of the bird flying, see here.
White-winged Black Tern
As always, there are some much better shots here, on the Birdguides website, or here, on the Sheffield Bird Study Group website.
This bird, and the accompanying Common Terns, were both "year ticks".
Year List update:
155 - White-winged Black tern
156 - Common Tern