The functionality and retention capacity of water reservoirs is generally impaired by upstream erosion and reservoir sedimentation, making a reliable assessment of erosion indispensable to estimate reservoir lifetimes. Widely used river gauging methods may underestimate sediment yield, because they do not record rare, high-magnitude events and may underestimate bed load transport. Hence, reservoir lifetimes calculated from short-term erosion rates should be regarded as maximum values. We propose that erosion rates from cosmogenic Be-10, which commonly integrate over hundreds to thousands of years, are useful to complement short-term sediment yield estimates and should be employed to estimate minimum reservoir lifetimes. Here we present Be-10 erosion rates for the drainage basins of six water reservoirs in Western Turkey, which are located in a tectonically active region with easily erodible bedrock. Our Be-10 erosion rates for these catchments are high, ranging from approximate to 170 to approximate to 1,040 t/km(2)/yr. When linked to reservoir volumes, they yield minimum reservoir lifetimes between 255 and 1,650360 years until complete filling, with four reservoirs having minimum lifespans of 110 years. In a neighboring region with more resistant bedrock and less tectonic activity, we obtain much lower catchment-wide Be-10 erosion rates of approximate to 33 to approximate to 95 t/km(2)/yr, illustrating that differences in lithology and tectonic boundary conditions can cause substantial variations in erosion even at a spatial scale of only approximate to 50 km. In conclusion, we suggest that both short-term sediment yield estimates and Be-10 erosion rates should be employed to predict the lifetimes of reservoirs.