The protection of watercourses from erosion is the most important and necessary intervention to any river in order to control the flow channel protecting in that way the riparian land uses. Erosion leads to soil leaching, desertification and downstream sediment transportation reducing consistently the river capacity. Initially, in this paper the soil erosion phenomenon, its determinant factors, as well as the usual protective measures taken are briefly analyzed. Then, the phenomenon of watercourses erosion, the slope stability calculation methodology and the applied interventions are presented in detail. Finally, given the corrosive phenomena in various places of Kalamas riverbed, especially among the settlements of Parakalamos and Mazaraki, the slope stability in this region is assessed. More specifically, an extensive description of the phenomenon is carried out, its causes are interpreted, suggestions of immediate protection measures are expressed and an estimation of the total cost of all necessary labor and materials is made, for completing the project.