Water Quality Index

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What is the WQI?
The Water Quality Index (WQI) is a single value that represents several combined measurements and is easily interpreted by managers, elected officials, and residents.

WQI calculation varies slightly for each monitoring program, as each program uses different parameters (measurements).

View Greensboro Water Quality Index Map below.

Stream Monitoring

The WQI calculation for streams consists of nine measurements, including temperature, dissolved oxygen (DO%), fecal coliform, biochemical oxygen demand (BOD), total phosphorus, turbidity, total suspended solids, total dissolved solids, and nitrate nitrogen. Each measurement is assigned a score from 0-100. The nine scores are then averaged to determine the WQI value. The WQI value for each stream site is assigned a score ranging from 0-100.

Good (80-100)
Above Average (60-80)
Average (40-60)
Below Average (20-40)
Poor (0-20)

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Benthic Macroinvertebrate Monitoring

The qualitative WQI rating for freshwater benthic macroinvertebrates is the same as the bioclassification rating, which is based on the type and number of species collected. Different benthic macroinvertebrate species have varying levels of pollution tolerance, which impacts their ability to survive in a particular stream based on the stream's conditions. The WQI value is calculated from the benthic monitoring sites across the state monitored by the NCDEQ.

For more information on bioclassification rating, visit NCDEQ's Biological Assessment Branch, and refer to the DWR Benthos Data.

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Habitat Monitoring

The WQI value for habitat considers stream conditions such as bottom substrate, shading, pool and riffle variety, and bank stability. The WQI value is calculated from the habitat assessment form created by the Division of Water Resources of North Carolina Department of Environmental Quality (NCDEQ) and is assigned a score ranging from 0-100.

For more information on the habitat assessment form, visit NCDEQ Biological Assessment Branch, and refer to the Standard Operating Procedure Manual.

Good (80-100)
Above Average (60-80)
Average (40-60)
Below Average (20-40)
Poor (0-20)

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Fish Community Sampling

The qualitative WQI rating for fish community sampling is the same as the North Carolina Index of Biological Integrity (NCIBI). The NCIBI is based on 12 factors, such as the type and number of species found, their age group, and whether signs of disease were observed.

For more information on the NCIBI, visit NCDEQ's Biological Assessment Branch, and refer to the Fish Community Assessment Data.

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