A river type commonly occurring in mountainous areas
whose sources of water include snowmelt and a series of coalescing springs
and tributaries. The benthic zone is strewn with smooth rocks, boulders,
gravel and sand. Few species of macrophytes can live there due to the
steep gradients and swift currents. Macro invertebrate communities typically
form food webs, and productivity is modest compared to limestone streams,
due to the slightly acidic pH of the water.