Maturation ponds use the ultra-violet component of natural sunlight for the disinfection of micro-organisms present in wastewater. The details of the mixing processes are still not well understood and clarification is required for optimal and reliable pond design. Temperature and radiation measurements were collected from a maturation pond in South-East Queensland and compared to a one-dimensional model to elucidate the dominant mechanisms for mixing and heat transfer. It was found that mixing in the pond follows a diurnal pattern of stable stratification during sunlit hours followed by downward mixing from the surface, eroding the stratification over several hours. Finally, a uniform vertical temperature distribution is established during hours of darkness. The dominant mechanisms for mixing are top-down natural convection during the evenings and wind shear during high wind-speed events. Radiation and molecular diffusion were found to be less significant to the heat transfer and establishment of stable stratification.