Middle Yakima River Basin Bacteria TMDL

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.

Our final plan

We have submitted the Mid-Yakima River Basin Bacteria Total Maximum Daily Load (TMDL) water quality improvement plan to the Environmental Protection Agency (EPA). This water quality improvement plan aims to address high bacteria levels in three sub-basins: Cowiche Creek, Moxee Drain, and Wide Hollow Creek. We held a public comment period from Oct. 13, 2020, through Nov. 13, 2020. The comments and our response to comments is included as an Appendix to the plan. We submitted the final TMDL to EPA for approval on Dec. 8, 2020. EPA approved the TMDL on Dec. 18, 2020. Once finalized and implemented, this plan should protect recreational uses in the watershed. You can view 2020 comments online in eComments.

Supporting Documents 

• Focus sheet
• Focus sheet (Espanol)

What we have done

We conducted several 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 started developing the Mid-Yakima River Basin Bacteria TMDL plan in 2015. We held a public meeting on July 28, 2015 to start the process. We held several Technical Advisory Work Group meetings throughout 2016. The project was prolonged due multiple staffing changes and the validation of data collected over such a wide time period. The final TMDL plan was submitted to EPA on Dec. 8, 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 water improvement 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 work with a wide range of partners who help conduct studies, serve on the advisory committee, participate in planning, and conduct or oversee cleanup activities. Also, we look forward to continuing to work 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; these buffers help filter out contamination
• 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 surface water
• Pick up pet waste, don't let rain wash it into our rivers and streams