The monograph describes research methods and geoecological assessment of polder lands. The history of research and practical use of surface waters of the Kaliningrad region is characterized, modern problems of their geoecological state are revealed. The characteristic of polder lands as complex natural and economic systems is given, the necessity of geoecological studies of the catchments of small rivers located on them is substantiated. A methodological approach has been developed to assess the geoecological condition of the basins of small watercourses through the combined analysis of hydrological, hydrochemical and geoecological data. Hydrological calculations of the key characteristics of the river flow of small watercourses of polder lands were carried out, the dependencies between them were revealed. Field studies were carried out, hydrochemical data sets were obtained on the rivers of polder lands for four hydrological seasons of 2020-2021. Retrospective hydrochemical information has been processed. The prevailing pollutants, integral indicators of water quality and the main sources of pollution are calculated. Based on the results obtained, a scheme of spatial distribution of pollution of the river network of polder lands is constructed. The geoecological condition of the basins is assessed on the basis of a complex of natural and anthropogenic data; based on the result obtained, recommendations for its improvement are given. It is of interest to specialists in the field of geoecology, hydrology, hydrochemistry, environmental management and environmental protection.