Rhithral streams
 

Rhithral headwaters are fed largely by seasonal snowmelt or originating as the outlet streams of lakes. They exhibit a wider temperature range; summer temperatures usually are between 5 and 10°C.
There are large seasonal but no large diel flow fluctuations, the bed normally is more stable than in most kryal streams.

The zoobenthos consists mainly of cold-adapted mountain stream species that occur over a broad range of elevation and that are at the upper limits of their altitudinal distribution. The flora usually consists of aquatic mosses, lichens, and a relatively diverse algal flora. Fishes are often present.