Turbines of high- and medium-head hydropower plants (HPP) can be heavily eroded by water containing suspended sediment particles. This leads to considerable maintenance costs, efficiency reductions and production losses. This problem was addressed in a SFOE pilot project at the high-head run-of-river HPP Fieschertal in Valais, Switzerland, from 2018 to 2021. Using an innovative combination of methods, the suspended sediment load, turbine abrasion and efficiency losses were measured and analysed in detail. Building on the previous projects since 2012, an unprecedented comprehensive data series over nine years was compiled. On this basis, models to predict abrasion on coated Pelton runners and their efficiency reduction were further developed and calibrated. Moreover, operational measures (temporary shutdowns of HPP in periods with exceptionally high suspended sediment loads) and refurbishment works were investigated to economically optimise the HPP operation. It is expected that the results of this project will contribute to increasing the energetic and economic efficiency of high- and medium-head hydropower plants on watercourses with increased sediment loads.