Temperature Standards and Criteria

Water temperature is an important element for the health and survival of native fish and aquatic communities. Temperature can affect embryonic development; juvenile growth; adult migration; competition with non-native species; and the relative risk and severity of disease. Complex lifecycles within the biological community require complex temperature standards. To best protect fish populations the Washington State surface water quality standards (Standards) now encompass a broader range of aquatic life temperatures, which reflect the intricacy of aquatic lifecycles throughout the year. Fish such as salmonid species, including bull trout, Dolly Varden, and Char now have more stringent temperature criteria. Redband trout and warm water fish like sucker, chiselmouth, and dace have less stringent temperature criteria.

At key life stages, such as adult migration and holding, spawning, incubation, rearing, and smoltification, salmonids have different temperature needs. The Standards accommodate these different needs with a range of uses. They identify specific stretches of streams and rivers where these uses occur. In areas where more than one use occurs, the most restrictive criteria apply. For a complete list of the different aquatic life uses and their associated numeric criteria see this table.

Temperature requirements are particularly critical during spawning and egg incubation periods. Those life stages need a cooler temperature to ensure that fertilized eggs have high survival success and the embryos develop into healthy emergent fry. For the window of time when that life stage occurs, the Standards apply more stringent temperature criteria to streams known to have spawning and egg incubation areas. The time frame varies depending on the geographic location and the subspecies present in the area. For example, in one area where salmon and trout are spawning and incubating eggs, the critical time period is February 15 - July 1. Outside that window of time (July 2 – February 14) the underlying less restrictive standard applies.

Complete list of time frames, temperatures and fish use


Brief description of Temperature in the Water Quality Standards


Guidance and Implementation of the temperature standards

EPA Region 10 Guidance

Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water Quality Standards Temperature Criteria Draft Discussion Paper and Literature Summary (Ecology publication)
Ecology's discussion document on changing the temperature standards.

Designating Waters for Native Char Protection (website)

Water Quality Program Guidance: Implementing Washington State Temperature Standards through TMDLs and NPDES Permits (Ecology publication)
Ecology's guidance on implementing the temperature standards in permits and TMDLs.

Methods to Reduce or Avoid Thermal Impacts to Surface Water: A manual for small municipal wastewater treatment plants (Ecology publication)
Methods to reduce or avoid thermal impacts to surface waters.

Dealing with Temperature Listings on The 303(D) List: Is There a Better Way?
Paper presented at the 2008 TMDL Conference.
WEF Manuscript Session 9a.pdf

Continuous Temperature Sampling Protocols for the Environmental Monitoring and Trends Section
Continuous temperature monitoring protocols used by Ecology's Environmental Assessment Program (EAP).

Water quality standards temperature guidance from nearby states

Surface Water Quality Standards: Temperature-Related Page on Idaho State's Department of Environmental Quality (web site)

Oregon Department of Environmental Quality (website)


For questions or comments, please contact:

Susan Braley
Water Quality Program
WA Department of Ecology
P.O. Box 47600
Olympia, WA 98504-7600
Phone: 360-407-6414
Email: SWQS461@ecy.wa.gov

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Last updated April 2016