Flow restoration and the impacts of multiple stressors on fish communities in regulated rivers

River regulation for hydropower is undertaken worldwide, causing profound alterations to hydrological regimes and running water habitats. Regulated catchments are often subjected to additional stressors, arising inter alia from agriculture, forestry and industry, which are likely to interact with impacts of river regulation on fish and other biota. Such interactions are poorly understood, hindering planning of effective mitigation and restoration.

We investigated fish responses to increased discharge (as a restoration measure) in regulated rivers in Sweden. We compiled electrofishing data from river channels downstream of hydropower dams, each of which either has or lacks a mandated minimum discharge corresponding to c. 5% of pre‐regulation discharge. We further analysed interactions between flow restoration and co‐occurring local and regional stressors.

River channels without a mandated minimum discharge were characterised by a low diversity of fish species with traits favouring ...