The article by Stuart E. Bunn and Angela H. Arthington, published in the *Cooperative Research Centre for Freshwater Ecology*, reviews the fundamental principles and ecological consequences of altered flow regimes on aquatic biodiversity. The authors highlight four key principles that link hydrology and aquatic biodiversity: 1. **Flow as a Determinant of Physical Habitat**: Flow significantly influences the physical habitat in streams, which in turn affects the biotic composition. This is evident at various spatial scales, from catchment to patch levels, and impacts the distribution and abundance of aquatic organisms. 2. **Evolutionary Adaptations to Natural Flow Regimes**: Aquatic species have evolved life history strategies in response to natural flow patterns. Altered flow regimes can lead to recruitment failures and biodiversity loss. 3. **Connectivity for Population Viability**: Maintenance of natural longitudinal and lateral connectivity is crucial for the viability of many riverine species. Barriers can isolate populations, leading to failed recruitment and local extinction. 4. **Invasion Facilitation by Altered Flow**: The alteration of flow regimes facilitates the invasion and success of exotic and introduced species. Water transfers between basins and disease spread are also mechanisms that enhance these invasions. The authors emphasize the need for more experimental research to better understand and predict the impacts of altered flow regimes on aquatic biodiversity, particularly in the context of land-use changes and water resource development. They argue that current knowledge is largely based on untested hypotheses and that more manipulative or experimental approaches are necessary to advance the field.The article by Stuart E. Bunn and Angela H. Arthington, published in the *Cooperative Research Centre for Freshwater Ecology*, reviews the fundamental principles and ecological consequences of altered flow regimes on aquatic biodiversity. The authors highlight four key principles that link hydrology and aquatic biodiversity: 1. **Flow as a Determinant of Physical Habitat**: Flow significantly influences the physical habitat in streams, which in turn affects the biotic composition. This is evident at various spatial scales, from catchment to patch levels, and impacts the distribution and abundance of aquatic organisms. 2. **Evolutionary Adaptations to Natural Flow Regimes**: Aquatic species have evolved life history strategies in response to natural flow patterns. Altered flow regimes can lead to recruitment failures and biodiversity loss. 3. **Connectivity for Population Viability**: Maintenance of natural longitudinal and lateral connectivity is crucial for the viability of many riverine species. Barriers can isolate populations, leading to failed recruitment and local extinction. 4. **Invasion Facilitation by Altered Flow**: The alteration of flow regimes facilitates the invasion and success of exotic and introduced species. Water transfers between basins and disease spread are also mechanisms that enhance these invasions. The authors emphasize the need for more experimental research to better understand and predict the impacts of altered flow regimes on aquatic biodiversity, particularly in the context of land-use changes and water resource development. They argue that current knowledge is largely based on untested hypotheses and that more manipulative or experimental approaches are necessary to advance the field.