Thermal and oxygen depth profiles in Lake Tinaroo were measured monthly at six sites over a two-year period from May 1988 to July 1990. Lake Tinaroo exhibits thermal layering throughout most of the year. Partitioning of the water column into an oxygenated epilimnion and a deoxygenated hypolimnion was well established by October each year. Breakdown of stratification occurred in late May to June and persisted until September. From October to May multiple thermoclines (diurnal, parent) developed, particularly during still weather. Localized disruption of stratification by oxygenated, cool, denser inflows during flood events in the catchment occurred during the rainy season. Thermocline tilting was noted after prolonged periods of south-easterly winds, with a deeper thermocline/oxycline at the north-westem end of the lake. South-westerly winds had a corresponding effect on the north-east of the lake. The distribution of oxygenated water and deoxygenated water, affected by seasonal stratification, thermocline tilting, upwelling and flood-mediated disruption of stratification, is of importance to recreational fisheries and the location of water intake points for urban and domestic use. Lake Tinaroo has thermal characteristics of outer tropical rather than equatorial tropical lakes, owing in part to altitude effects.