The north and south basins of Windermere in the English Lake District, UK, support autumn- and spring-spawning populations of Arctic charr, Salvelinus alpinus, which have been studied since the 1930s. Continuous investigations of the population dynamics of Arctic charr at this lake have involved gill netting since 1939, collection of fishery catch-per-unit-effort data since 1966, and hydroacoustic surveys since 1990. Analysis of these and associated long-term data on the abiotic environment and other components of the fish communities revealed recently contrasting fortunes of the Arctic charr populations of the north and south basins, the latter of which has been significantly impacted by eutrophication while both basins have shown elevated water temperatures and increasing roach, Rutilus rutilus, populations. Despite the introduction of phosphate stripping in 1992 and some subsequent initial improvement, the hypolimnion of the south basin still remains significantly eutrophicated and the fishery catch-per-unit-effort in this basin is now at record low levels. In addition, the spatial distribution of roach has expanded to form significant components of the fish communities of inshore and offshore surface habitats, where this cyprinid may compete with Arctic charr for zooplanktonic prey. It is concluded that the Arctic charr populations of Windermere, particularly those of the south basin, currently face a number of significant environmental pressures and continued management action is required to ensure their survival.