The chemical characteristics of the water of Lake Moondarra, an artificial lake in tropical north-western Queensland, are described. Changes in ionic composition, and in the concentrations of major nutrients and heavy metals, were monitored over a 12 month sampling period. Seasonal variations within the lake were strongly influenced by climatic conditions, principally rainfall which affects run-off and dilution by way of the intermittently flowing river and creeks. The results show that, in spite of the considerable input of nutrients, their concentration in the lake waters remains consistently low. The heavy metal concentrations in the lake water are also well below the limits regarded as acceptable for drinking water.