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The Onyx River flows for over 30 km from its source in the Greenwood Valley, to discharge into endorheic Lake Vanda. It is the only significant source of meltwater, and hence allochthonous nutrients, to the lake. In recent years localised climatic change has resulted in an increase in the annual discharge in the river from 2.5x10(6) m(3) (1970s and early 1980s) to 5.5x10(6) m(3) (late 1980s and early 1990s). In order to better understand the potential consequences of increased river flow to nutrient loading to the lake, we undertook a series of studies in 1993/94 to identify the sources and sinks of nutrients within the Onyx River system. Concentrations of dissolved inorganic and organic nutrients varied both with time and with distance down the river. During early flows the river water was rich in nutrients, with nitrate nitrogen reaching over 1500 mg m(-3) and dissolved reactive phosphorous 27 mg m(-3). This appeared to reflect two sources, freeze concentration of nutrients in the stream bed over winter, and selective enrichment with nitrate, probably via atmospheric deposition. Another source of nutrients during early flows was leaching from freeze damaged cells in microbial mats. However during these early flows much of this water did not reach Lake Vanda, but rather was lost to lateral groundwater recharge. During the main flow period, nutrients came predominantly from glacial melt, though nitrate enrichment persisted for several weeks. Water reaching Lake Vanda during the main flow period always had low concentrations of nutrients relative to source water. Two microbially active zones were identified which appeared to be responsible for nutrient stripping. These were Lake Brownworth at the head of the river and the "Boulder Pavement", some 4 km upstream of Lake Vanda. There was no relationship between discharge and nutrient concentrations and for most of the year a linear discharge:loading curve was found. Increased flows into Lake Vanda will therefore increase the nutrient loading, but have little effect on concentrations of nutrients in lake water, at least over the range of discharge seen in this study.