Surface deterioration of concrete occurs at the waterline of many hydraulic structures in contact with soft water in cold regions. Progressive disintegration of the surface leads to exposure of the coarse aggregate and ultimately of the reinforcing steel. Mechanical, physical and chemical processes could cause deterioration of concrete at the waterline. The objective of this study was to investigate experimentally the effects of interactions between leaching, frost action and abrasion on the surface deterioration at the waterline of hydro power structures. The test methods were designed to represent the environmental conditions at the existing Swedish hydro power structures as accurately as possible. Air-entrained concrete with a water-to-cement ratio (w/c) of 0.54 and non-air-entrained concrete with a w/c ratio of 0.62 were used in the experiments. It was demonstrated that the amount of damage caused by interactions between the three degradation mechanisms exceeded the total amount of damage caused by the mechanisms separately. Moreover, leaching significantly amplified the effects of frost action and abrasion for both concrete mixes. Considering the exposure conditions at Swedish hydro power plants, it was concluded that leaching combined with frost action accounts for most of the superficial damage observed at the waterline of these structures.