March Browns are the first large mayflies of the year to emerge. Members of the clinger mayfly family, March brown nymphs live in riffles and fast, rocky runs. They are very flat and almost triangular in shape with gills protruding from their abdomen. Nymphs are so well adapted to their environments that they are rarely found in drift until emergence.
Traditional tight line Nymphing or nymphs under an indicator is the best way to imitate the March Brown Nymph.
Focus on fast water and make sure your nymphs are on the bottom!