Water Quality Improvement Project
Palouse River Toxics Study

Historical data from Ecology and USGS studies indicated high levels of certain chlorinated pesticides and PCBs in Palouse River fish. The contaminants of concern pose a risk to people that consume the fish. However, the amount of data available was limited and dated. A fish tissue study was conducted by Ecology in 2005 to give a better understanding of the extent and severity of the problems.

During May through August 2005 Ecology collected fish samples from the mainstem, north fork and south fork Palouse Rivers. Fish were caught using an electro-backpack shocker and nets. The fish species collected included largescale suckers, northern pike minnows, chiselmouth, carp, and smallmouth bass. Fillets from these fish were analyzed to determine the level of chlorinated pesticides and PCBs. In addition, Ecology conducted a stormwater study in the city of Pullman. This study took place during the winter of 2005-2006.


The good news is that the results of the fish tissue study indicate that the levels of chlorinated pesticides and PCBs have declined substantially over time. Some of the levels are now within human health criteria and others are very low.

A TMDL report detailing how the Palouse River will achieve water quality standards for PCBs and dieldrin (the only chlorinated pesticides still above standards) was completed and submitted to the Environmental Protection Agency (EPA). EPA approved the TMDL on November 9, 2007.


The TMDL relies on:

  • The natural decline of these chemicals over time.
  • Stormwater control activities.
  • Agricultural methods and best management practices that reduce sediment runoff.
  • Investigation of old landfills as a possible source.
  • Limits placed the amount of these pollutants in wastewater treatment plant's discharge.


Technical Information


Last updated February 2016


WRIA: #34 (Palouse)
County: Whitman

Water-body Names:
Palouse River

Chlorinated pesticides

# of TMDLs:
PCBs and chlorinated pesticides: - 4

PCB and chlorinated pesticides TMDL - approved by EPA.
Toxics study - under development

Contact Info:
Elaine Snouwaert
Phone: 509-329-3503
Email: Elaine.Snouwaert@ecy.wa.gov

Eastern Region
Department of Ecology
4601 N Monroe Street
Spokane, WA 99205-1295