A dolichopodid, or long-legged fly, one of many I saw in the irises on the north shore of the large lake. They were flitting about in the foliage along the water's edge and occasionally landing on floating leaves and even on the surface of the water. Normally it would be almost impossible to identify such a small fly to the species level just from photos but, in this case the dark band and white tips on the wings indicate that this is a male Poecilobothrus nobilitatus (family Dolichopodidae, order Diptera). The white wing-tips seem to be used to signal to the the females during courtship, as shown in this video by Harry Rutherford.
A bit further along my walk, well away from the waterside, in an area of long grass and sparse woodland, I came across another dolichopodid fly (either a female P. nobilitatus or another species of dolichopodid fly) with a bright red parasitic mite attached to its leg. In spite of its added burden, the fly seemed to get around reasonably easily.
Photos taken in Reading University grounds, Reading, UK, on 2009-07-10.