Among the existing state cadastres, an important place belongs to the water, which is the basis of state management of the water fund. According to the Water Code of Ukraine, the water fund includes all water bodies, provides for the systematic determination of reserves and quality of water resources in a particular area.Water quality is affected by a large number of factors, including location, water body category, water intake area, water mirror area, water volume, river network type, terrain parameters and properties, hydrological conditions. No less important is the influence of anthropogenic factors, which is correlated with the degree of development of the territory, land structure, population and settlements, man-made load and so on. The purpose of the work is to analyze the state of watercourses in the Syan river sub-basin and to establish the main factors that affect water quality. The quality of water resources has a great impact on public health, so a careful analysis of the state of natural water sources is one of the important components of the cadastre of water resources. Method. During the research we worked with information provided by the Lviv Hydrometeorological Service, Lviv egional Department of Water Management, research laboratories engaged in monitoring and analysis of water resources of Lviv region for the last ten years, data from the environmental passport of Lviv region for 2020. During processing of results used a combination of methods of system and structural analysis, analytical comparison, mathematical formalization, cartographic materials, which provided the ability to solve problems and achieve the goal and the reliability of conclusions [Sovhira S. V. et al., 2016]. Results. It is established that the water quality in watercourses flowing through the territory that does not carry a man-made load depends mainly on natural factors, namely: territorial location, climatic conditions, relief, hydrogeological and geomorphological conditions, etc. Due to climate change, various natural phenomena and problems with flooding are increasingly occurring, which negatively affect water resources and quality. Floods occur for various reasons and, in recent years, are characteristic of the Syan river sub-basin, especially in mountainous areas. For the territory characterized by high economic development, the water quality of rivers depends: on mining activities; soil pollution; creation and operation of artificial reservoirs; economic activity within the floodplainchannel complexes; dredging and channel-directing works; deforestation and intensive economic activity at watersheds, which is clearly confirmed by the state of water in the Shklo river and its tributaries Gnoyanets, Tereshka, etc. Data on the state of watercourses in the Syan river sub-basin were collected, systematized and analyzed using and adhering to the main provisions of the integrated approach to water resources management according to the basin principle. Scientific novelty and practical significance. It is proposed to use an integrated approach to create water resources management plans based on the basin principle on the example of the Syan river sub-basin. This approach will allow to identify all sources of influence, their nature, relationship and interaction and to fill with official, relevant data geoportal “State Water Cadastre” on the website of the State Water Agency.