Epirh(e)ithral and metarh(e)ithral streams

Upper and middle reaches of montane and upland streams, characterised by turbulent, irregular flow, by diurnal and annual temperature variations higher than in the crenon (unit C2.16), and by aquatic biocoenoses largely dominated by Turbellaria, Ephemeroptera, Plecoptera, Trichoptera, Diptera, by Bryophyta and epilithic Bacillariophyta, Cyanophycaea, Rhodophyta and Chlorophyta algae, with few, specialised, emergent macrophytes (units C2.25-C2.28). The unit corresponds to the -Trout zone- or -Salmonid zone- of western European ichthyological classifications.