This paper presents the monitoring results of a reinforced concrete gravity dam affected by alkali-aggregate reaction (AAR). The reinforced concrete dam comprises the right-wing dam, the water intake/powerhouse, the spillway, and the left-wing dam. The total crest’s length is about 1030 m and the maximum height above foundation is about 41 m.   This dam was built in three phases namely in 1932, 1952 and 1961. Shortly after its completion, permanent concrete displacement due to AAR was noticed. The evolution of AAR pathology varies along the dam according to the construction phases. To mitigate excessive concrete degradation and to release the consecutive compressive stress state due to AAR expansion of the concrete, vertical slot cutting of the dam has been performed.   The dam has been instrumented, among other instruments, with pendulums and a geodetic and levelling network capturing the dam’s behaviour since the early 1970s. Monitoring instruments recorded both vertical and horizontal deformations of the dam before, during and after slot cutting. The downstream-upstream movement in about 60 years recorded an upstream drift of 53 mm at the right-wing and a downstream drift of 91 mm at the left-wing dam. The vertical displacement of the crest for the same period reached 100 mm upwards at the left-wing dam. The paper will present in detail the deformation of the dam affected by the AAR swelling and the alleviation resulting from the mitigation measures taken to extend the service life of the dam.