Hydropower schemes alter existing hydrological regimes and the aquatic ecosystems that are dependent on them, and so require sound planning, investigation, siting, design, mitigation, monitoring and adaptive management. Issues that can arise include water quality, sedimentation, abundance and quality of habitat. The challenges are to adequately understand ecosystem components and function, minimise creation of new impacts through siting and design, include mitigating measures and monitor and respond t issues as they arise. The inter linkages with social and economic aspects of sustainable hydropower must also be well understood.