After 2019, irrigation operations at the Land Treatment System (LTS) in the Whakarewarewa Forest are scheduled to cease. A number of options and locations have been considered for the discharge of the treated wastewater when the current discharge consent ceases. Following consultations and technical assessments, the preferred option of Rotorua Lakes Council is to upgrade the existing plant to a full Membrane Bioreactor Plant with the addition of an Ultraviolet Disinfection System (or alternative treatment to achieve an equivalent performance in terms of treated wastewater quality). Under this arrangement, wastewater would be subjected to biological, chemical and physical treatment processes, and the treated wastewater discharged through Te Arikiroa Thermal Channel to Sulphur Bay. Rotorua Lakes Council is thus undertaking an environmental impact assessment study to determine the effects of discharging treated wastewater to the thermal channel and Puarenga Bay (Lake Rotorua), with particular reference to aesthetic, water quality and ecological considerations. These considerations include potential effects related to faecal indicator bacteria, nutrient concentrations, metals, dissolved oxygen, and taonga species (native species of cultural significance). The assessment focused on: (i) The projected treated wastewater characteristics; (ii) Existing conditions of the receiving water; (iii) The sensitivity of the receiving water and the impact of the proposed discharge on water quality and taonga species (native species of cultural significance) in Te Arikiroa Thermal Channel and Sulphur Bay. The main techniques used to inform the assessment in this study were: 1) Analysis of historical water quality data, 2011-2014; 2) Collection of additional water quality data at Te Arikiroa Thermal Channel and Sulphur Bay and along a transect to quantify spatial variability (sampling in 2016 and 2017); 3) Mass balance dilution modelling to predict water quality in the Te Arikiroa Thermal Channel and Sulphur Bay (Lake Rotorua), at a site outside of the assumed mixing zone; 4) Lake ecosystem modelling conducted by Abell et al. (2015) to assess effects related to eutrophication; 5) Background review of biological information and field investigations for taonga species at Sulphur Bay and Te Arikiroa Thermal Channel (2017).