| In 1970, the National Sanitation
Foundation developed the Water Quality Index (WQI), a standardized
method for comparing the water quality of various water bodies. In Iowa, the
WQI is calculated by using eight
common water quality parameters (dissolved oxygen, fecal coliform bacteria,
pH, 5-day BOD, total phosphorus,
nitrate-nitrogen, turbidity, and total dissolved solids). Values range from
0 – 100 and streams are classified as poor
(0-25), fair (25-50), medium (50-70), good (70-90), or excellent (90-100).
WQIs were calculated on the streams
monitored monthly as part of Iowa’s Ambient Water Monitoring Program. For
2000-2005, 81% of the streams had a
WQI in the medium category while the remaining 19% were in the good
category.
Streams in Iowa show seasonal WQI patterns. For the majority of streams, water quality is medium
during the
spring, followed by a decline in water quality during the summer months when even more streams fall
from the
good category into the medium and fair categories. During the fall, nearly half the streams exhibit
medium
water quality while the rest have good water quality. Water quality is at its best during the winter
months, with
nearly 69% of the streams classified as good.
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