An experimental DNA-tracking technique was used to get a handle on where all of the fecal contamination in the Yakima River was coming from.

The Granger Drain watershed dumps into the Yakima River and is dotted with dairies. Many people have assumed that most of the contamination was coming from area dairies. However, before making changes, the South Yakima Conservation District wanted to gain an understanding of where the E.coli contamination was originating.

The DNA-tracking technique uses fingerprints from manure at each dairy to compare to the fingerprints found in the Granger Drain. The resulting report does show that cows are still the largest single source of E.coli bacteria. But just 31 percent of all samples were linked to cows.

Another interesting finding is that there were approximately equal proportions of “manageable sources” such as cows as there are “unmanageable sources” such as wild animals.

Here’s how the list of top contributing sources of contamination breaks down.


  • 31 percent of all samples were linked to cows.
  • 14 percent of all samples were linked to birds.
  • 11 percent of all samples were linked to humans.
  • 7.5 percent of all samples were linked to rodents.
  • 7.5 percent of all samples were linked to deer and elk.
  • 6 percent of all samples were linked to raccoons.



Although cows make up the single largest source of contamination they are by no means the only source of contamination. Past cleanup efforts have focused on eliminating waste runoff from dairies. That’s because regulators considered human and wildlife waste as “very minor” contributors to the problem. However, in light of this new evidence regulators may have to alter clean up plans.

Although the study conducted is not 100 percent foolproof, it does give regulators more insight into contamination sources than they had before.

For more details from this story, please see the Tri-City Herald. (James, link to:
http://www.tri-cityherald.com/news/2002/0625/story1.html)

Tri-City Herald