The Environmental Requirements (ERs) for closure at Ranger Uranium Mine stipulate that the minesite and associated natural waterbodies must be rehabilitated to a state which allows them to be incorporated into the surrounding Kakadu National Park. Water quality closure criteria are being developed in response to these requirements. The closure criteria aim to provide a management approach that allows water quality to remain within a range that will not compromise the long-term environmental objectives of the area. Turbidity is one of a number of measures for which closure criteria for receiving waters, including billabongs and stream channels adjacent to the Ranger minesite, are being developed. Research conducted at Georgetown Billabong, adjacent to the mine, has revealed a distinct relationship between turbidity and chlorophyll-a, the latter an indirect measure of primary productivity. This relationship has been assessed over several years (1981, 2009, 2012 and 2013) to identify turbidity threshold values associated with reduced primary production. The threshold values will be evaluated against existing and separate macroinvertebrate response data derived from creek channels to develop closure criteria which represent biological change, rather than simply water quality change. Thresholds so far identified are consistent with literature values reported for turbidity effects upon aquatic organisms and suggests sustained exposure in the range 30-50 NTU results in reductions in chlorophyll-a.