Hydrological risks induced by human activities case study: the water pollution of Trotuş River. The antropic impact on the water resources from the Trotuş drainage basin is manifested on a quantitative dimension - through the readjustment of the river network and the extraction of important quantities of water used in different socio-economic activities; and on a qualitative one - through the modification of some physical, chemical and biological water properties (done through numerous spilling of polluting substances from domestic, industrial or agricultural sources). In the present study we have tried to analyze the main polluting sources of Trotuş River, the pollution degree and the quality state of the water for the 1983-2001 period, on the basis of the data derived from four water quality monitoring stations situated on the river: Ghimeş-Făget, Târgu Ocna, Adjud and Vrânceni. At the same time, the analysis of the number of cases when the maximum admitted limit for 1^st quality degree waters has been exceeded has relieved that the ecological accidents occurrence risk is maintained at high values. And this in the situation when after 1991, on account of an economical reorganization and an improvement of the degree of the treatment of the industrial and sewage waters, a reduction of the water pollution cases and a water quality improvement has been registered.