Declining fish communities characterise global freshwater environments, including those in Australia. Lost river connectivity through water resource development is a key cause of decline, disrupting fish migrations and threatening species productivity, viability and fisheries. Millions of dams, weirs and lesser barriers arising from water resources projects, road and rail transport and hydro-electricity schemes obstruct fish passage in rivers worldwide. Fishways are in place at few sites in Australia and globally relative to the numbers of barriers, and few mitigate the effects of barriers adequately. Most constrain the passage of fish communities and few have performed effectively when assessed against appropriate biological standards. Herein we focus on Australian experience within the global context of obstructed fish migrations, declining fish biodiversity and inadequate fishway performance. We review the migratory characteristics of Australian freshwater fish, identify the effects of different in-stream barriers and other habitat changes on the four classes of migratory behaviour and note how Australia's highly variable hydrology presents particular challenges in mitigating fish passage barriers. Mitigation options include: basin-scale approaches; improved management of barriers, environmental flows and water quality; barrier removal; and development of improved fishway designs. Mitigation of fish-passage problems can aid in adapting to climate change effects, reversing fisheries declines and rehabilitating fish communities.