This document describes the extensive geodetic system used to monitor a 185-meter high arch dam in Southern Africa as part of the Lesotho Highlands Water Project. The system includes a triangulation network with primary and secondary pillars, precise leveling, traverses with hanging and inverted pendulums, and altimetric wires to measure horizontal and vertical displacements of the dam. Adjustments of the network using least squares indicate mean errors generally under 1 mm. Displacements measured include horizontal movements up to 16 mm between summer and winter and vertical movements up to 4.3 mm.