Presented are the first data of a structural analysis of the river basins in the Upper Angara region, and the spatial features of the distribution of the values of the structural indices for the third-order basins are determined. As a representative area for identifying the structural features of the river basins in the low-water karst region, we used the basin of the Oek river (the right tributary of the Kuda river). Using the methodological approach based on the Horton analysis, we determined the main structural indices of the basin, namely, bifurcation indices, lengths, areas, slopes and geomorphic work, for third-order basins. Mapping of the territory used the technique of automated identification of catchment basins in terms of SRTM v.4 DEM, followed by data processing in the SAGA GIS. An analysis of the distribution of the indices showed the largest dissection of the western part of the basin in the upper components of the erosion network. It is determined that the highest homogeneity of the structural indices is characteristic for the third-order sub-basins located in the western part of the Oek basin within the Irkutsk-Cheremkhovo plain, while the largest diversity in the diversity of the structural indices corresponds to the basins of the Kuda depression. An analysis of the distribution of the indicators of geomorphologic work showed that a significant part of the matter transport is done by the first-order channels in the western part of the basin. An analysis was made of the territory for the distribution of the basins with a different potential to accumulate/remove matter. According to this indicator, most of the basins are defined as transit basins, and the accumulation basins occupy one-third of the territory and are concentrated within the Irkutsk-Cheremkhovo plain in the lower part of the basin. Two releasing basins, small in area, are located in the northern part of the basin.Keywords: Upper Angara region, stream order, structural analysis, structural indices, DEM, accumulation basins, releasing basins.