The surface expression of the Waimangu Geothermal System comprises hot springs and steaming ground which occur in the vicinity of volcanic craters that formed during the 1886 Tarawera Rift eruption. Boiling chloride spring waters discharge over a 30 m vertical interval from the Steaming Cliffs along the western shore of Lake Rotomahana (similar to 340 m asl) to inferno Crater (373 m asl) in the upper Waimangu Valley. K-Na and K-Mg ratios, aqueous silica concentrations and Delta O-18((sulfate-water)) values of spring waters, indicate deep equilibration temperatures that range from 200 to 280 degrees C, while uniform B/Cl ratios (similar to 0.0075) suggest the chloride waters derive from a single reservoir. Stable isotope data are best explained as the result of boiling and dilution in the upper part (<2 lan depth) of the system, with an interpreted parent liquid composition of Cl=585 mg/kg, delta(18)O = -4.75 parts per thousand, and delta D = -37.5 parts per thousand. This liquid is distinct from the parent inferred for the nearby Waiotapu geothermal system and is positively enriched in both delta(18)O and delta D compared to focal meteoric water (delta(18)O = -6.85 parts per thousand, delta D = -42 parts per thousand). Boiling upflow is interpreted to dominate beneath all surface features except in the vicinity of Lake Rotomahana, where a cold hydrostatic cap (similar to 100 m thick) depresses the temperature gradient of rising fluids discharging at Steaming Cliffs. The effects of ground water dilution generally increase with hot spring elevation in response to a steepening hydraulic gradient and rugged topography associated with the volcanic craters of Waimangu Valley. A minimum chloride Bur estimate of 80-100 g/s corresponds to athermal output of 150 to 190 MW.