Water Quality Assessment Categories

The water quality assessment list divides waterbody impairments into the following categories:

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 project (also known as a 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 features and there must be some legal or financial guarantee that they will be implemented.
- 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 conditions.
Category 5 - Polluted waters that require a TMDL: the traditional list of impaired water bodies traditionally known as the 303(d) list. Placement in 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 are required for the water bodies in this category.

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.

Last updated June 2011