Subsurface hydrothermal activity dominates the heat and salt budgets of the deep water column in Crater Lake, Oregon. From a time series of conductivity-temperature-depth data and data from a thermistor chain mooring, we estimate that the net hydrothermal heat flow is ~1 W m-2 and the corresponding salt flux is ~5 μg m-2 s-1. This paper discusses the observation of these fluxes and the mechanisms and time scales of mixing responsible for the redistribution of these properties through the water column. Free convection and wind mixing homogenize the upper 200 m of the lake twice annually. Deep-lake ventilation occurs during early winter and to some extent during late spring. However, since the deep lake does not reach atmospheric saturation with respect to dissolved oxygen at any time during the year, ventilation of the deep water appears to be incomplete. During periods of seasonal stratification, the active input of hydrothermally enriched fluids produced heterogeneities and instabilities in the density structure of the deep lake that may drive deep-lake mixing. As a result of these and other mixing processes, Crater Lake remains relatively well mixed, despite its great depth. ¿ American Geophysical Union 1993