Water Quality Improvement Project
Wilson and Cooke Creeks:
Fecal Coliform


The Wilson Creek sub-basin is east of the Cascade Mountains in Kittitas County, Washington State. It drains most of the area surrounding the city of Ellensburg, as well as the agricultural lands and forests to the north and east of the city. The climate in the sub-basin area is semi-arid, with an average annual rainfall of 8.9 inches. The sub-basin covers approximately 244,500 acres (394 sq. miles) of land.

Land uses in the sub-basin vary from forestland, range, and intensively irrigated agriculture to urban and suburban areas. The sub-basin contains a network of supply canals, diversions, irrigation return drains, and numerous natural creeks, such as Cooke Creek. Water from the Yakima River is directed through the sub-basin by three large irrigation supply canals. The sub-basins’ natural creeks are ultimately used as the conduits for irrigation return flows.

Water quality issues

Studies indicated that the downstream portion of various creeks in the Wilson Creek sub-basin violated Washington State water quality standards for fecal coliform bacteria. (See Study Area map)

Why this matters

Fecal coliform is a type of “bacteria” common in human and animal waste. It can make people sick and cause the closure of shellfish harvesting beds. Bacteria can get into our waters from untreated or partially treated discharges from wastewater treatment plants, from improperly functioning septic systems, and from livestock, pets and wildlife.

People can help keep bacteria out of the water. Keep livestock away from creeks and implement best management practices (BMPs) to prevent runoff from agricultural fields. Properly collect, bag, and trash dog poop. Check your on-site sewage system to make sure it is maintained and working properly.

Status of the project

Ecology, with the help of local groups, developed a total maximum daily load (TMDL) report. The report included results of water quality studies and monitoring; recommendations for helping the water quality to meet the state water quality standards; and an implementation strategy to determine how to accomplish the recommendations. Ecology sent the finalized TMDL to EPA for approval. EPA approved the document in July 2005.

The national pollution discharge elimination system (NPDES) permits issued to the city of Kittitas after September 30, 2006, had more stringent requirements for fecal coliform bacteria levels in the waste water than previously. The city also upgraded its municipal wastewater treatment plan. Concentrated animal feeding operations (CAFOs) are not allowed to discharge pollutants to the waters of the state except under extreme circumstances. A single load allocation was set for all non-point sources of fecal coliform pollution in the sub-basin. Human contribution of fecal coliform bacteria was expected to be reduced through implementing BMPs.

Technical information

Unless otherwise specified the following documents are Ecology publications.

Wilson Creek Sub-Basin Bacteria Total Maximum Daily Load (Water Cleanup Plan): Submittal Report

Wilson Creek Sub-basin Bacteria Total Maximum Daily Load Detailed Implementation Plan

Wilson Creek Sub-Basin Fecal Coliform Bacteria Effectiveness Monitoring Water Quality Study Design (Quality Assurance Project Plan)

Wilson Creek Sub-basin Bacteria Total Maximum Daily Load: First Water Quality Post TMDL Monitoring Report

Related information

Focus on Wilson Creek Sub-basin Bacteria TMDL

WRIA 39: Upper Yakima Watershed Information (Water web site)


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Last updated June 2015
  Water resource inventory area (WRIA) 37 map, Washington State.


#39 (Upper Yakima)


Water-body Name:
Cooke Creek
Wilson Creek

Fecal coliform bacteria

# of TMDLs: 16

TMDL approved by EPA
Has an implementation plan
Post-TMDL monitoring report

Contact Info:
Greg Bohn
Phone: 509-454-4174
Email: Greg.Bohn@ecy.wa.gov

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