This paper presents the pre-construction evaluation of the ground for the Lake Mead Intake No 3 Tunnel and the experience gained from the project, which had the aim of maintaining water supplies for the Las Vegas greater metropolitan area. The construction of this tunnel using a dual-mode slurry shield represents a major engineering achievement, which pushed back the boundaries of closed shield tunnelling: Overcoming an extended fault zone under high hydrostatic pressure in the metamorphic rocks and mucking-out difficulties associated with high rates of water inflow in the sedimentary rocks necessitated closed-mode operation over about 2 km at unprecedentedly high face pressures of up to 14 bar.