Abstract:Dam construction providebenefits to local communities including hydropower generation and flood protection, but also harmsfish species by altering physical habitat andproviding pollution during the construction process. Evaluating river reaches habitat suitability level mayknow how the habitat and which extentaffected by dams. This study used a systems analysis approach to preliminarily evaluate habitat suitability level at before dam construction and during dam construction in Kraal River. A habitat model which included hydrodynamic and pollution transportwas used to evaluate theGarra fish (Garrapingi) habitat suitability level affected by pollution produced by dam building system and living waste water. Flow velocity, water depth, riverbed substrates and pollution concentrationwere selected as suitability indicators. Numerical model simulations were undertaken as follows:Firstly, the water depthand velocity were simulated and thesubstrate distributions were also surveyed. The pollution concentration was simulated and the corresponding suitability indexes were calculated based on the fish preference curves.After that, the HSI distributions in both before dam building and during dam building were obtained and compared.The results shown that the pollution from dam building system were severely influenced the Garra fish habitat. It is worth noted that the habitat suitability can be recover when thedischarge pollution concentration could reduce lower than 800mg/L.