Publication Summary

Turbidity, total suspended solids (TSS), fecal coliform bacteria, and pesticide samples were collected from several sites in the Wilson-Cherry sub-basin of the upper Yakima River from April to October 1999. The data generally showed that headwater streams and supply canals met Class A criteria, but that water quality was soon degraded as range and agricultural lands were crossed. The Cherry Creek branch supplied twice the TSS and fecal coliform bacteria loads of the Wilson Creek branch.

Water quality data were collected from April through October 1999 in the Wilson and Cherry Creek sub-basin as part of the upper Yakima River suspended sediment and organochlorine pesticide total maximum daily load (TMDL) assessment. Sites were located on tributary branches within the sub-basin in various land use types.

Water samples were analyzed for total suspended solids (TSS), turbidity, and fecal coliform bacteria. Some samples also were analyzed for Escherichia coli bacteria, Klebsiella bacteria, or a suite of 107 pesticides. Turbidity and basic loading, as well as TSS and fecal coliform bacteria, for each site were calculated for each site.

Canal water and headwater streams entering the sub-basin generally met Class A water quality criteria. Water quality became highly degraded in most of the streams and return drains before they crossed south of the Vantage Highway. Some tailend water from canal systems also had poor water quality. Turbidity values, suspended sediment concentrations and loads, and fecal coliform bacteria significantly increased in range and agricultural areas of the sub-basin, especially in the Cherry Creek watershed. Urban areas appeared to have less impact on these contaminants during the April to October monitoring period.

Correlations investigated were not reliable to predict fecal coliform loads or counts from TSS or turbidity values. The 1999 concentrations of 2,4-D, dicamba, and MCPA appeared to have increased since 1995. Diazinon was not detected as it was in 1995, and atrazine and bromacil concentrations appeared to be of similar or lower concentrations than in 1995.

The resulting summary and comparison of TSS, turbidity, fecal coliform, and pesticides should help water quality managers focus their continuing water quality improvements in the Wilson and Cherry Creek sub-basin.

Link to EIM data for User Study ID UPYAK