Dam constructions negatively impact river ecosystems by altering hydrologic regimes and connectivities. River continuum theory provides a useful framework for considering the specific influences of dams on the ecohydrology of river systems. This study presents a Transitional Region Concept for analysing the nature of hydrologic changes resulting from dam constructions and how these changes relate to the life history and ecology of the fish. The stream ecosystem of the transitional region is subdivided into a four-dimensional framework. The framework consists of spatial structure, matter structure, energy structure, and hydrological process. The characteristics and variations in this framework, as affected by dam construction on the Yangtze River, are quantitatively assessed. The spawning ground of the Chinese Sturgeon (Acipenser sinensis), located in inertial zone of the river ecosystem, is used as the study site. Current and historical hydrological data are used to determine the effects of dam construction on the spawning grounds of Chinese Sturgeon in the river. The results show that the Three Gorges Reservoir (TGR) has a significant impact on the suitability of the spawning grounds of Chinese Sturgeon. This could also affect the prey/predator species dynamics and the sturgeon fish population in especially the lower reaches of the Yangtze River. The findings of this study could provide critical considerations for policy makers and river managers to protect Chinese Sturgeon from the adverse effects of the TGR. Copyright © 2010 John Wiley & Sons, Ltd.