The article examines the main features of the hydrographic network of the Republic of Karelia and briefly assesses the main natural factors that determine them (geological structure, topography, climate, geographical location of the republic). The characteristics of waterbodies (lakes, storage reservoirs) and watercourses (rivers, streams) and their specific features are recounted. Their size distribution and the quantitative parameters of the main objects are given. The main regional feature of the hydrographic network of Karelia – lake-river systems is considered (through the example of the largest – Kovda system). Data on water reserves, water resources, and the main features of their hydrochemical composition are presented. It is shown that the total river flow resources in the republic are 1.3-fold higher than the national average per 1 km² and 3-fold higher per inhabitant. Thus, the supply of surface water resources in Karelia is quite high and their quantities are not a factor limiting the development of the republic’s economy (even taking into account the intra-annual fluctuations of river flow). The problems existing with water supply to the population and some economic facilities are either of organizational and technical nature, or are associated with below-standard water quality of natural sources. Transformations of the hydrographic network under human impact are shown using the example of the White Sea-Baltic Canal and the Vygozero-Onda reservoir. The impact of hydrographic features and water resource availability on economic development and the main water and environmental problems is evaluated. The most significant among these features are low water content, high gradient and large rapids of rivers, a large proportion of lakes, significant reserves of surface water resources versus relatively low groundwater resources, a very specific “Karelian” type of water quality.