Water Quality Assessment Categories
The water quality assessment list divides waterbody impairments into the
- Category 1 - Meets tested standards for clean
waters: placement in this category does not necessarily mean that a
water body is free of all pollutants. Most water quality monitoring is
designed to detect a specific array of pollutants, so placement in this
category means that the water body met standards for all the pollutants for
which it was tested. Specific information about the monitoring results may
be found in the individual listings.
- Category 2 - Waters of concern: waters where there
is some evidence of a water quality problem, but not enough to require
production of a water quality improvement (WQI) project (including
total maximum daily load [TMDL])
at this time. There are several reasons why a water body would be placed in
this category. A water body might have pollution levels that are not quite
high enough to violate the water quality standards, or there may not have
been enough violations to categorize it as impaired according to Ecology’s
listing policy. There might be data showing water quality violations, but
the data were not collected using proper scientific methods. In all of these
situations, these are waters that we want to continue to test.
- Category 3 - Insufficient data: water where there
is insufficient data to meet minimum requirements according to Policy 1-11.
Category 4 - Polluted waters that do not
require a TMDL: waters that have pollution problems that are being
solved in one of three ways:
- Category 4a - has a TMDL: water bodies that have an
approved TMDL in place and are actively being implemented.
- Category 4b - has a pollution control
program: water bodies
that have a program in place that is expected to solve the pollution problems.
While pollution control programs are not TMDLs, they must have many of the same
elements and there must be some legal or financial guarantee that they will be
- Category 4c - is impaired by a non-pollutant: water
bodies impaired by causes that cannot be addressed through a TMDL. These
impairments include low water flow, stream channelization, and dams. These
problems require complex solutions to help restore streams to more natural
- Category 5 - Polluted waters that require a
TMDL or other WQI project: the traditional list of impaired water bodies
traditionally known as the 303(d) list. Starting with the 2008 Water
Quality Assessment, Washington’s 303(d) list of polluted waters were placed under Category 5 in the
this category means that Ecology has data showing that the water quality
standards have been violated for one or more pollutants, and there is no
TMDL or pollution control plan. TMDLs or other approved WQI projects are required for the water bodies in
Why is a stream listed in more than one category?
A single water body segment may be listed multiple times, depending on how
many tested pollutants violated the water quality standards. For example, a
water body tested for a group of pollutants might be listed in
category 5 because temperatures consistently violated standards; in category
2 because some high bacteria counts were found, but not enough to list it as
impaired; and in category 1 because dissolved oxygen levels were good. Each
listing will also include the medium in which the pollutant was
measured—water, sediment, habitat, or tissue.
Contact us for more information
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