Our study is aimed at determining the hydrodynamic changes of mountain stream channels caused by degradation that was initiated by uncontrolled mining of bed material. The study was conducted on Mszanka and Targaniczanka streams in which the collected data included: longitudinal profiles, cross-sections of the channels, the geometry of bed forms and analysis of particle composition of the bed material. The results show that hydrodynamic parameters have changed downstream from the studied sectors and along the cross-sections. Bed degradation also was linked to bank erosion, which intensified morphological changes of channels effecting the spatial distribution of flow velocity, shear stresses and stream power. The investigation also demonstrated that the bedload movement was in accordance with channel changes and more sediments were deposited than transported along the studied area. Finally, local aggradation and unstable channel capacity were observed.