Effects of river regulations on the fauna living in the rapid regions of the River Stora Lule Alv, which is influenced by the Suorva Reservoir since 1927. The conditions in the natural river system of the river Lilla Lule Alv are compared. The changed rhythm in which the water runs off caused by the regulation is explained by several examples of natural rivers. As opposed to the unregulated river Lilla Lule Alv the river Stora Lule Alv shows abnormal glaciation with radical influences on the topography of the river bottom and its flora and fauna. The damming up of snow and glacier melting waters cause essential divergences from the natural development of temperature in regulated rivers, disturbing the vital function of the organisms. Investigations on the way in which the waters run off dammed and natural lakes show, taking into consideration the "Organic Drift" and the bottom fauna, the negative consequences of the regulation on the rapid regions below power dams. An experiment at the power dam of Selsforsen showed that by taking plankton rich surface water also below power dams a rich bottom fauna can live in the river.