Sunlight is considered as the most important factor for disinfection in Waste Stabilisation Ponds (WSP) based on many studies. High rate algal ponds (HRAPs) are advanced pond systems for which high disinfection performance has been reported, however, the mechanisms of disinfection in HRAPs are not well understood. In this paper two separate experiments were performed to gain understanding about sunlight and dark disinfection processes in HRAPs. The first experiment was conducted to model the MS2 removal efficacy under different environmentally relevant regimes of UVB irradiance in buffered distilled water. It is concluded that, for these environmentally relevant UVB irradiances: the inactivation rate of MS2 phage increased rapidly from 0.01 to 1.24 h^-1. The die off rate was K=0.2887 h^-1/W/m² (R²=0.9851). The second experiment assessed the influence of a range of typical environmental temperatures, from 10- 30ºC, on the dark die-off rate of MS2 and Escherichia coli in mixing unfiltered wastewater for 6 days. The results show that the dark die-off rate of MS2 and E. coli increased significantly with increasing temperature(P<0.0001).