Results collected and analysed by the Global Environmental Monitoring System on Water (GEMS/Water) over the last two decades for biological oxygen demand (BOD), alkalinity, nitrates and phosphates are indicative of efforts undertaken in various parts of the world to assess freshwater quality.

BOD is an indicator of the organic pollution of freshwater. In comparing the past two decades, rivers in Europe and Australasia show a statistically significant reduction in BOD concentrations. Although the reduction is not particularly large, it is indicative of positive trends. There was no change in the assessed results for North America, although there was a tighter data distribution, indicating the data available for 1991-2000 is less variable than for previous periods.

Alkalinity (as CaCO₃) was analysed for all sampling stations available at the continental level. Concentrations remained reasonably steady between the two decades for Africa, Asia, South America and Australasia. Significant increases in alkalinity concentrations were noted for European and North American rivers, which may indicate a shift towards reduced acidic impacts at the continental scale.

Examination of the outflow stations in 82 monitored river basins indicated a decrease in bicarbonate concentrations between the two decades in the northern latitudes, including North America, Europe and Asia.

For the period 1976-1990, European rivers displayed the highest concentrations of calcium at the continental level. Concentrations varied from between 2 mg per litre and 50 mg litre for major rivers. Comparing the two decades, observations of surface water showed an increase in calcium concentrations in the Laurentian shield region of North America, and in the rivers of the North Central European region.