Krenal stream
 

Krenal streams, fed by ground water, occur at all elevations. They provide relatively constant and benign conditions - relatively warm and clear water, and stable substratum.
Near the source, the temperature typically varies only 1-2°C over an annual cycle, making spring brooks summer-cool and winter-warm habitats. The inhabitants of perennial springs are not subjected to freezing or desiccation.

The relatively benign and stable environmental conditions of well-oxygenated krenal streams result in higher zoobenthic densities compared to kryal and rhithral habitats. Insects predominate in alpine spring brooks, whereas amphipods, isopods and molluscs play a more important role at lower elevations. In general, insects predominate in the zoobenthos of high altitude streams.