The University of Waikato was requested by Bay of Plenty Regional Council to quantify the effectiveness of the Ohau diversion wall when controlling the Kaituna River outflow during high and low flows. The Ohau diversion wall was constructed to divert nutrient-enriched water from Lake Rotorua away from the main basin of Lake Rotoiti and towards the Kaituna River outflow. Bay of Plenty Regional Council wished to determine whether controlling the Lake Rotoiti outflow to enable rafting on the Kaituna River would impact on the efficacy of the Ohau diversion wall. The Kaituna River is used for commercial and recreational white-water rafting and kayaking, and is a proposed venue for the 2013 World Rafting Championships. However, control of the Kaituna outflow to regulate the water level in the lake may conflict with the use of the Kaituna River for rafting, which requires discharge to be between minimum and maximum raftable flows (13 m³ s⁻¹ and 26 m³ s⁻¹, respectively). Outflow from the lake may be controlled so that flows in the river are within the raftable range for a number of hours a day, and then adjusted for the remainder of the day to prevent high or low water levels. However, it is possible that this may affect the efficacy of the Ohau diversion wall, leading to concerns that this mode of operation could impact on the water quality in Lake Rotoiti. To address these concerns, three-dimensional hydrodynamic modelling was used to quantify the transfer of water from the Ohau channel to Lake Rotoiti under scenarios that facilitated rafting operations. The model was set up so that a tracer (transported by water flow) would be released in the Ohau inflow for the duration of the simulation. Tracer concentrations were output from the model simulations as depth profiles for five stations in the lake to quantify the transport of water from the Ohau channel into Lake Rotoiti.