C. splendens is common along slow-flowing streams and rivers in central Europe. This sp. is well-suited for studies on the population structure and mobility of semi-aquatic rheobiont organisms. In this study the authors investigated a local population over a 2 km stretch of river in central Germany, by habitat analysis and mark-recapture-experiments. Emergent aquatic vegetation only influences density if the coverage is lower than 10%. Adult damselflies mainly use vegetation along the banks. Unused, moderately eutrophicated stands of herbaceous vegetation without trees and shrubs are preferred. Insolation in the morning is the primary factor for the selection of males' territories and thus determines the pattern of density. The investigated population turns out to be much bigger than expected. 2649 individuals have been marked individually (1543 6, 1106 9). 47% of the 66 and 29% of the 9 9 have been recaptured at least once. Most individuals migrated less than 300 m, which is roughly the home range size, but 23 individuals covered more than 1000 m. Three bridges spanned the investigated stretch of river. None of them caused a complete fragmentation of the habitat, but in the case of a wide but low bridge, more than 70% of the approaching damselflies turned back. However, 13% of all recaptured individuals successfully crossed at least one bridge.