frazil
A collection of stray ice crystals that form in fast-moving water.
countable, uncountable
It has been suggested that it may be due to the accumulation of frazil or anchor-ice.
Where it comes from
From Canadian French frasil, frazil, fraisil, from French fraisil (“coal cinders”), from Old French faisil.
Adapted from the Wiktionary entry frazil (CC BY-SA 4.0).