Water Quality Improvement Project
Wenatchee River Area:
Dissolved Oxygen & pH

Water quality issues

The federal Endangered Species Act lists the Upper Columbia River Chinook salmon and Upper Columbia River steelhead trout as endangered, and the Upper Columbia River bull trout as threatened. Phosphorus levels in the Wenatchee River affect the dissolved oxygen (DO) and pH levels in the river. Phosphorus enters the Wenatchee River via point sources (for example, wastewater treatment plants and fish hatcheries) as well as nonpoint sources (for example, on-site septic systems, abandoned or closed landfills, or livestock with access to streams).

Why this matters

Oxygen dissolved in healthy water is vital for fish and aquatic life “breathe” to survive. It is more difficult to transfer oxygen from water to blood than it is to transfer oxygen from air to blood. Therefore, it is critical that an adequate amount of oxygen is maintained in the water for this transfer to take place efficiently and sustain aquatic life. Oxygen is also necessary to help decompose organic matter in the water and bottom sediments as well as for other biological and chemical processes.

pH is a measure of how acidic or alkaline the water is. The pH is measured on a scale of 0-14, with the lower numbers indicating acidic conditions and higher numbers alkaline conditions. Optimal pH levels to support fish and wildlife should range from 6.5 to 9.0. A pH of 7 is neutral.

pH can affect the solubility of nutrients and metal compounds. By affecting the solubility of nutrients, it can change the amount of nutrients available for plant growth. If too many nutrients are available, aquatic plants can grow out of control. When these plants decompose, they can deplete the water of oxygen. The solubility of many metal compounds also changes greatly with pH. Generally, a reduction in pH (more acidic) increases the solubility of heavy metals. When more metals are dissolved in the water, aquatic animals may absorb them faster. Therefore, a lower pH (more acidic) may make these metals more toxic to aquatic life.

Status of the project

The Washington State Department of Ecology (Ecology), in cooperation with citizens in the Wenatchee River watershed, is developing a total maximum daily load (TMDL) to determine how to bring the quality of the water in the Wenatchee River to state standards for DO and pH. Meeting the water quality standards for DO and pH in the watershed will protect the water for the various uses of the citizens living in the watershed. It will also help to protect the endangered and threatened salmonid species, as well as other important aquatic species. To achieve this goal, large reductions of point sources and nonpoint sources of phosphorus loading to the Wenatchee River and Icicle Creek must occur.

Ecology completed a technical study of the Wenatchee River watershed in 2006. Ecology, along with a citizen advisory committee, developed a water quality improvement report (WQIR) covering the DO and pH issues in the watershed. The WQIR contains the technical study including results and recommendations, and an implementation strategy. The implementation strategy lays the foundation for what citizens and communities in the watershed will do to reduce phosphorus loads to the Wenatchee River. Reducing phosphorus going into the river should improve the DO and pH levels in the river.

After addressing comments from the public review and comment period, Ecology sent the WQIR to the Environmental Protection Agency (EPA). EPA approved the WQIR in August 2009.

Technical information

Unless otherwise specified, the following documents are Ecology publications.

Addendum to Wenatchee River Watershed Dissolved Oxygen and pH Total Maximum Daily Load

Wenatchee River Watershed Dissolved Oxygen and pH Total Maximum Daily Load: Water Quality Improvement Report (revised)

Quality Assurance Project Plan: Wenatchee River Temperature, Dissolved Oxygen, pH, and Fecal Coliform Total Maximum Daily Load, Year 1 Technical Study

Quality Assurance Project Plan: Wenatchee River Temperature, Dissolved Oxygen, pH, and Fecal Coliform Total Maximum Daily Load, Year 2 Technical Study

Wenatchee River Basin Dissolved Oxygen, pH, and Phosphorus TMDL Study

Related information

Reducing Phosphorus Pollution to Improve Water Quality (Water Quality web site)

WRIA 45: Wenatchee Watershed Information (Water web site)


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Last updated June 2015
  Water resource inventory area (WRIA) 45 map, Washington State.


WRIA(s): #45 (Wenatchee)
County: Chelan

Water-body Name:
Wenatchee Basin

Dissolved Oxygen

# of TMDLs: 9

Approved by EPA

Contact Info:
Lynda Jamison
Phone: 509-575-2434
Email: Lynda.Jamison@ecy.wa.gov

Central Region
Department of Ecology
1250 West Alder Street
Union Gap, WA 98903-0009