Nymphs are actually sinking artificial flies. They imitate fly insects which live under water, especially at the bottom. There are various ways for fly fishing with them also different indicators for fish bites. Some fishermen prefer indicators other work with the behavior of the line. Nymphs are indispensable in certain situations. Mainly trout is found its food under the water. The river chub in the cold days also looking for food in the water and on the bottom of the basin.