A geographically variable water quality index used in Oregon

An Oregon Water Quality Index has been developed which takes into account differences in water quality resulting from geographical characteristics of separate basins. The index was developed for the purpose of providing a simple, concise, and valid method for expressing the significance of regularly generated laboratory data. The trend-monitoring value of the index was demonstrated for two quite different Willamette River stations. Correlations among this and several other proposed indexes averaged 0.87. Yearly and seasonal variations in water quality were quantitized and found to average 88.9 and 78.9 Oregon Water Quality Index units for the higher and lower water quality stations respectively over the period 1971-1976. Calculated rates of change in water quality were +0.68 and +0.91 Oregon Water Quality Index units/year for the two stations for 1971-1976. The Oregon Water Quality Index is now used routinely in Oregon's primary station sampling program to recognize water quality trends.