River shaped by lake outflow
One of the types of flowing water specified by LAWA is type 21: lake outflow shaped flowing waters . This is a type that is independent of the ecoregion and occurs both in the young moraine area of the north German lowlands (subtype 21_N) and in the Alpine foothills (subtype 21_S).
Water structure
The sections can always be found below lakes. In their structure, they differ greatly depending on the location. They are usually wider and more open than the sections below and often have a reed belt . The current is usually strongest directly at the lake outflow. There is often relatively little dead wood, but a lot of gravel or sand, but this depends heavily on the respective geological conditions.
Flora and fauna
The biocenosis of these waters is strongly influenced by the lake's influence on temperature and material balance. The special natural features take a back seat. Living things have to be adapted to high temperatures, fluctuating oxygen levels and a high proportion of nutrients. In invertebrates, filter feeders such as large mussels, black flies and filtering species of caddis fly larvae are mainly found. There are mostly unspecialized fish species such as perch or roach , and to varying degrees also sea-dwelling fish.
There are floating leaf plants , spawning herbs and frog-bite plants as well as reed plants in the bank area. Very narrow, tree-lined lake outflows are partly also free of vegetation. Plankton is often present due to the inflow from the lake.
Examples
- Parts of Schwahn, Havel and Mildenitz (e.g. below the Goldberger See ) (North German lowlands)
swell
- Profile of river type 21 at wasserblick.net (PDF file; 146 kB) accessed on November 22, 2011