The aquatic larvae of the Diptera are often the most abundant and most diverse group of the benthic macroinvertebrate fauna.
They are able to survive in and colonise practically all freshwater habitats, and some species can tolerate harsh environmental
conditions. They are therefore both a qualitatively and quantitatively important group of biological indicators for assessing freshwater
systems. On the other hand their determination at the species level is very difficult. This is in part due to a lack of taxonomic
work in the group, but also the absence of comprehensive determination keys, that meet the needs of water managers. As
a result, the aquatic larvae of the Diptera often play a subordinate role in water management. In light of the EU Water Framework
Directive the present work is a first step in improving the integration of the important group of the Diptera in water management
practice: a comprehensive determination key, which is geared at water managers. The key includes 60 taxa, largely at the family
and genus level. In contrast to already existing keys the present work tries to differentiate the taxa on the basis of simple and
user-friendly characters. Numerous figures allow for easy checking of determination results. The key is applicable in Germany,
Scandinavia, Great Britain and the Benelux states. Mainly taxa from running water systems are considered, but the key can also
be used at the family level to determine taxa from standing water bodies.