Most attempts to assess the pollution of rivers have beenbased on analyses of the dissolved component of riverwaters. This is usually because of concerns about drinkingwater supplies or because water quality data may be directlyrelated to potentially toxic effects in organisms. However,audits of water quality are likely to be inconclusive unlessmeasurements are made over long periods of time andunder a range of conditions. Variations in river discharge andpollutant sou rce areas, irregular pollutant emissions, andchanges in temperature and pH and Eh, can all result in large,short-term fluctuations in water quality. Unfortunately, longtermand temporally detailed monitoring of river waters isboth costly and time consuming. In Australia in particular,the highly variable nature of river regimes means that longrecords of discharge and water quality are required beforereliable interpretations are possible. Moreover, water qualitydata alone rarely reflect all the possible adverse effects ofpollution on aquatic biota. One reason for this is that theinteraction of organisms with the river environment is notrestricted to the direct uptake of pollutants from the water.In particular, contamination of the channel bed and toxicityof suspended particulate matter may both have seriousconsequences for the ecology of aquatic systems.