The purpose of the paper is to describe the practical application of scientific research on Lough Conn, a top class trout lake in Ireland. The main work carried out is enforcement of fishing laws, control of predators (pike) and competitors (perch), Stream development and water quality control which is the principal subject covered by the paper. Despite rigorous enforcement of water pollution laws, Lough Conn suffered from a major eutrophication problem in 1990. Following two separate studies by biologists, a number of measures were put in place to redress the situation. The Regional Fisheries Board immediately intensified inspection of farmyards throughout the catchment and, in conjunction with other agencies, commenced regular weekly sampling of 13 feeder streams and rivers to the lake with a view to pinpointing any increase in phosphate loadings. Both projects are ongoing. The Board has also been working with a State peat harvesting Company to reduce deposits of peat silt and is liaising closely with the forestry authorities to ensure that run-off of silt, fertilisers etc. from afforestation work is kept to a minimum. Sewage plants and septic tanks around the catchment are also regularly inspected. The objective of this paper is to illustrate the practical aspects of fisheries management in lreland and the extent to which the findings of scientific research are applied in practice.