Middle Yakima River Basin Bacteria TMDL

Wide Hollow Creek, Cowiche Creek, and Moxee Drain are three tributaries to the Yakima River near the city of Yakima. These tributaries are on the Washington state list of impaired water bodies, known as the 303(d) list, due to excessive fecal bacteria. We are developing a water quality improvement project in the area to control harmful bacteria sources and bring these tributaries back into compliance with state water quality standards.


Water quality issues

In many areas of the Mid-Yakima River Basin, fecal coliform bacteria and E. coli numbers are much greater that the maximum allowed under state water quality standards, and those numbers are significantly higher between April and October than during the rest of the year.

There are multiple potential sources of bacterial contamination in the middle Yakima River basin, such as:

  • Wildlife feeding and habitat areas.
  • Livestock on commercial and non-commercial farms.
  • Rural, residential, commercial, industrial, and urban stormwater runoff.
  • On-site septic systems and illicit sanitary connections.

What we have done

We conducted field surveys in the Cowiche Creek, Moxee Drain, and Wide Hollow Creek sub-basins from December 2004 through March 2006; from June through December 2010; and from March through June 2014. We used the data collected during these surveys to develop reach-specific bacteria loading capacities for each tributary, and estimated load reductions necessary to meet these capacities.

We developed a draft Mid-Yakima River Basin Bacteria TMDL report for this project. A public meeting on the project was held on July 28, 2015. Several Technical Advisory Work Group meetings were held throughout 2016. We are opening a comment period for this report in September 2020.

Status of the project

The final version of the report is being prepared and will be submitted to the Environmental Protection Agency (EPA) for approval later in 2020.

Why this matters

High levels of bacteria pollution in streams and lakes are a risk for disease to humans and animals that are exposed to contaminated water. Washington State is required to protect the “most sensitive” beneficial uses found in water bodies, which include the ability to wade, swim and fish in the state’s lakes, rivers and streams.  This clean up project will specifically reduce bacteria pollution within the Cowiche Creek, Moxee Drain and Wide Hollow Creek sub-basins.

What actions can help reduce fecal coliform bacteria and E. coli?

Ecology staff are working with a wide range of partners who help conduct studies, serve on the advisory committee, participate in planning, and conduct or oversee cleanup activities.  We also look forward to working with all residents of the project area.  Some key actions that groups and individuals can take to help reduce bacteria include:

  • Improve stormwater management practices
  • Protect existing streamside (riparian) buffers, and plant new ones where possible. Riparian buffers filter contaminated runoff
  • Identify and renovate failing septic systems
  • Modify livestock management practices to reduce animal contact with surface water
  • Improve irrigation practices to reduce the transport of bacteria into adjacent surface water
  • Provide public education regarding pet waste management