Kryal stream
 

Kryal streams are characterized by very low temperatures. At the snout of a glacier, emerging meltwater is close to 0°C, but temperature increases downstream. Where the summer maximum temperature exceeds about 4°C is considered the downstream limit of the kryal biotope.
Further characteristics of glacial streams are high turbidity and large diel flow fluctuations in summer resulting from freeze-thaw cycles, unstable substratum, an extremely short growing season and barren rocky shores.

Kryal streams are inhabited by a very restricted zoobenthos and only very few alga. With changing abiotic conditions, a typical downstream change in the fauna can be observed.