The Mayfly is a member of the Ephemera family, there are three mayflies commonly found in the British Isles, these are Ephemera danica, Ephemera vulgata & Ephemera lineata, for the purposes of this email we are treating them all as one (as the differences as negligible). Mayflies can be found in both still running water, but the majority are found on our rivers, it does not seem to matter the strength of the flow. Mayflies are found throughout the British Isles in all types of river and stream. They are easily identified in May and June as they will be the biggest up-winged fly on the water and white in colour. Mayflies can range quite considerably in size, from 15 to 25mm long (usually a size 14 to size 10 hook).