Inland Fisheries

3.1.2 Rhithron zones

Characteristics of rhithron zones

          They tend to show an alternation between (i) steep, narrow and shallow riffles or rapids, and (ii) flatter, wider and deeper reaches, termed pools. Riffles have high, turbulent flow, coarse bottoms of boulders, rocks or pebbles and limited attached vegetation. Pools have lower flow, bottoms of somewhat finer material and some rooted vegetation. This zone is characterized by turbulent flow and relatively low temperatures. Generally, the water is highly oxygenated, but at low water the pool and riffle system may break up into a series of pools, whose waters may become completely depleted of oxygen.