Background The River Wye has historically been the most productive river in Wales for Atlantic salmon (Salmo salar). However, in recent decades numbers have declined to around 15% of previous levels. Though present throughout most of the river catchment, salmon are unable to survive in its strongly acidic headwaters. Many of the problems affecting the health of the overall river system arise in the uplands of mid-Wales. These lead to highly acidic streams, flash floods, siltation, over-shading by trees and pesticide pollution downstream, which adversely impact fish and other Habitats Directive listed species. While individual problems are well-understood, it is only by addressing them at the catchment level that real improvements in water and habitat quality can be achieved. Objectives The ISAC 08 project built on the work of previous river restoration projects, such as Natura 2000 Rivers (LIFE99 NAT/UK/006088), to address the restoration of the Irfon catchment in mid-Wales. The project’s main objectives included the restoration of the hydrology of the upper catchment and the implementation of conservation measures for Atlantic salmon (Salmo salar) and several Annex II Habitats Directive species: white-clawed crayfish (Austropotamobius pallipes), freshwater pearl-mussel (Margaritifera margaritifera), lampreys (Petromyzon marinus, Lampetra fluviatilis, Lampetra planeri) and bullhead (Cottus gobio). The restoration programme included tree management to reduce over-shading of the river, the exclusion of livestock to reduce siltation, and habitat improvements for target species. Results The ISAC 08 project achieved its aim of protecting target species within the River Irfon using an ecosystems approach, to help the River Wye Special Area of Conservation (SAC) achieve favourable conservation status. It addressed the problems of water acidity, damage to streams caused by livestock, siltation and over-shading of rivers. Hydrological restoration in the upper Irfon catchment was initiated through land purchase, the removal of conifers, the infilling of forestry drains and by adding lime (ground limestone at 20-40 tonnes/ha) to ameliorate the effect of acid runoff. The latter measure provided a cost-effective method for correcting the problems associated with acid waters. The project changed how forest areas were managed to the benefit of rivers. Conditions for wildlife were also enhanced along 30 km of rivers by excluding livestock, introducing woody debris to enhance habitats, and reducing the shade from riparian woodlands. The project restored a total of ten hydrological source areas. The method developed by the project partners for improving habitats led to immediate and substantive increases in salmon numbers in upland streams. Restoration actions on some 10 km of river Natura 2000 network site (SAC) that included liming resulted in a measurable recovery in young Atlantic salmon numbers. As a result of the project, it was estimated that there were an additional 66 000 salmon parr (1-4 year old fish) in the upper reaches of the river. However, bullhead failed to colonise the upper reaches of the river and this is probably due to natural barriers and slower colonisation. There is evidence that restoration work will support an increase in the population of brown trout (Salmo trutta) and macro-invertebrates in the upper catchment. It was not possible to confirm project targets for additional sea lamprey and brook/river lamprey due to difficulties with sampling methodology, which could not be used in areas where woody debris was added to riverbeds. The project has also effectively opened up four to six new territories for European otter (Lutra lutra), which have re-colonised the upper reaches of the river as salmon numbers have increased. Working with Natural Resources Wales (NRW) at Abercynrig hatchery, ISAC established a captive breeding centre for white clawed crayfish, which utilises a methodology developed during the project. By the end of the project, about 2 500 one year-old crayfish had been introduced to streams in the SAC. The project confirmed that the River Irfon is a key site for freshwater pearl mussel in Wales; new populations were identified though there was no evidence of recent recruitment. Captive breeding of the mussel was established and their introduction will be a long-term project led by NRW. The threat of smothering by fine silt should have been reduced by the project’s habitat restoration work. Due to increased light arising from the removal of riverside trees, the aquatic Ranunculus habitat (3260) is expected to expand; all tributaries of the lower Irfon now have reservoirs of this habitat type. Fencing work also helped to protect 2 ha of alluvial forests with Alnus glutinosa habitat(91E0), and had an indirect effect in starting the restoration process on 23.5 ha of degraded afforested blanket bog. The project helped to change Welsh Government policy on the planting of forests on deep peat, and the blanket bog at the top of the Irfon is now an important site for peatland restoration. The project demonstrated the benefits of a catchment-based partnership of NGOs and statutory agencies in delivering improvements under the Habitats Directive and Water Framework Directive. Among the resulting socio-economic benefits, sport fishing has benefited from the improved water quality. Salmon have a substantial economic value and this should give the project a significant payback in the long-term. Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).