EPA - Ireland's Environment, An Integrated Assessment - 2020

Ireland’s Environment – An Integrated Assessment 2020 Topic Box 7.3 River Barriers Removing barriers improves river continuity for fish passage. Barriers have been installed in rivers from the earliest of times and have served many purposes from aiding navigation (e.g. locks) and harnessing river power (e.g. water mills and electricity generation) to creating reservoirs and amenities for water sports. The presence of a physical barrier across a river can prevent the movement of both biological organisms and sediment. Barriers can prevent the movement of migrating fish trying to get to their spawning grounds and the transport downstream of sediment needed to replenish lower reaches. In some cases, in summer, water trapped behind a barrier can reach temperatures that can harm aquatic organisms. Conservation monitoring of protected species such as salmon, shad, lamprey and the European eel show the damage caused by barriers impeding the upstream migration of these species. Such barriers are a major impediment to achieving the conservation objectives for shad and migratory lamprey in Irish rivers designated special areas of conservation under the Habitats Directive. In many cases, the ideal solution would be their complete removal. However, the social and economic benefits provided by barriers does not always permit this, and before a barrier can be removed an assessment is required to understand the full impact of removal. There may also be environmental reasons for not removing a barrier. In some situations, for instance, the presence of a barrier may prevent the spread upstream of invasive species. For example, the presence of natural and artificial barriers is considered important in protecting some Arctic char populations in Irish lakes from the impact of invasive fish species (Connor et al. , 2019). Several nationally and EU-funded research projects are looking at barriers and how various mitigation measures can be used to improve river continuity and the functioning of natural processes such as fish migration and sediment transport (e.g. the EU Horizon 2020 project AMBER – Adaptive Management of Barriers in European Rivers; the EPA- funded Reconnect barriers project; and the Interreg-funded Catchment CARE project. Inland Fisheries Ireland is undertaking studies to identify and locate barriers and develop guidance on mitigation strategies that can be examined and implemented. A selection of these barriers will be prioritised for a national mitigation programme under the next National River Basin Management Plan (2022-2027). A barrier that has been ameliorated by the construction of a fish passage The importance of free-flowing rivers has been recognised in the European Commission’s recently adopted Biodiversity Strategy for 2030, which has set a target of restoring at least 25,000 km of rivers as free-flowing watercourses by 2030 through the removal of obsolete barriers and the restoration of floodplains and wetlands. 176