Hydropsychidae as bio-indicators.

The applicability of single species as bio-indicators for the characterization of running waters is investigated. For this, species of the family of Hydropsychidae (Trichoptera) are chosen. Ten species have been recorded for the Dutch fauna, but some of them have disappeared and others are restricted in their distribution nowadays. Several authors have established a distribution pattern of Hydropsychidae according to a zonation from source to large river. In The Netherlands we could use this scheme only in small, fast running streams. For the characterization of lowland streams more data on the fauna are required. In the large rivers only one species is occurring (Hydropsyche contubernalis), increasing in numbers during the last decade. Probably a certain improvement of the water quality of the river Rhine is responsible for this.