Beautiful China-mark Nymphula nitidulata
Wingspan 18-22 mm.
One of the more distinctive and beautiful members of the Pyralidae, this is another species whose larvae are aquatic, feeding on bur-reed (Sparganium) and other water plants.
Found fairly commonly around lakes, rivers and ponds throughout Britain, the moths are on the wing during July and August.
It flies in the evening and at night, and comes readily to light.