This graduation thesis deals with the turbidity in the streams, which is result of natural erosion processes in river catchment, but lately more often caused by human water use and activities on the water. The consequence of cloudiness is not only a visual change of the water but it also effect on the physical and chemical properties of water and consequently the ecological characteristics of water. In this paper I presents hydrological monitoring of turbidity in Slovenia. It is given an overview about the problems of turbidity in the streams and factors that cause pollution and the consequences of changes in ecological conditions. I described some examples about the problems in our country and around the world.