<Li> The potamon is the remaining downstream stretch of river . It has warmer temperatures, lower oxygen levels, slow flow and sandier bottoms . </Li> <P> The International Scale of River Difficulty is used to rate the challenges of navigation--particularly those with rapids . Class I is the easiest and Class VI is the hardest . </P> <P> The Strahler Stream Order ranks rivers based on the connectivity and hierarchy of contributing tributaries . Headwaters are first order while the Amazon River is twelfth order . Approximately 80% of the rivers and streams in the world are of the first and second order . </P> <P> In certain languages, distinctions are made among rivers based on their stream order . In French, for example, rivers that run to the sea are called fleuve, while other rivers are called rivière . For example, in Canada, the Churchill River in Manitoba is called la rivière Churchill as it runs to Hudson Bay, but the Churchill River in Labrador is called le fleuve Churchill as it runs to the Atlantic Ocean . As most rivers in France are known by their names only without the word rivière or fleuve (e.g. la Seine, not le fleuve Seine, even though the Seine is classed as a fleuve), one of the most prominent rivers in the Francophonie commonly known as fleuve is le fleuve Saint - Laurent (the Saint Lawrence River). </P>

What is the middle section of a river like