ElĪbieta Jekatierynczuk-Rudczyk Abstract Hydrological and hydrochemical analyses in the Jaroszówka river basin were carried out in hydrological year 2003. The quality of the Jaroszówka water is characterized by the lowest level of transformation of physical and chemical composition among the Biaáystok rivers. Specific pollution load, which was discharged from the catch- ment to the Jaroszówka riverbed was much smaller than the load discharged to the main Biaáystok waterway (Biaáa), but was similar to the load of the small urban ri- vers (BaĪantarka and Dolistówa). A lower degree of the Jaroszówka spring water transformation demonstrates a significant role for pollution that flows directly to the riverbed. Key words: water quality, urban river, urban springs, specific pollution load. 1. Introduction Degradation of the environment is one of the most important problems of the modern world. Deterioration of water quality, which leads to decreased usability, has become a problem, especially for industrialized and urbanized areas (Cheámicki 1997). Biaáystok is the largest city of northeastern Poland (population 280 000), and almost the entire city is located in the basin of the Biaáa River - the left tributary of the SupraĞl River. The northern section of the city is drained directly by the SupraĞl River and its two small tributaries (the Jaroszówka is one of them); whereas the southern section is drained by the Horodnianka, a tributary of the Narew (Podziaá hydrograficzny Polski 1983). The flowing waters of Biaáystok are exposed to various kinds of pollution. The primary sourc- es of pollution are municipal and industrial sew- age discharged into the water from point, linear or diffuse sources. Municipal pollution is above all fuelled by domestic sewage. It is a mixture of household waste, physiological excretions of humans and domestic animals, and other sub- stances. Industrial pollution in the form of indus- trial sewage is channelled into rivers, streams, lakes, or groundwater. The sewage quantity and composition depends on the type of industry present in the region. In the Biaáystok region, the main sources of industrial sewage and pollution are the food processing industry (this type of sewage is rich in organic compounds, for exam- ple, lactic acid), textile industries, whose sewage contains dyes and phenols in addition to organic compounds, and power plants that discharge heat into surface waters (Raport 2004). In urban areas, point sources of pollution include sewage that is Vol. 8 No 1, 77-87 2008 Threats to a small river and its urban catchment: Hydrological and hydrochemical assessment of Jaroszówka River in Biaáystok, Poland Department of Hydrobiology, Institute of Biology, University of Biaáystok, ul. ĝwierkowa 20B, 15-950 Biaáystok, Poland e-mail: rudczyk@uwb.edu.pl