Results and Conclusions

Are Rivers Meeting Water Quality Standards?

TEP has determined discovered that lower sections of four of the five main rivers in the Tillamook Bay watershed routinely violate Oregon's water quality standard for recreational contact.  These rivers are the Miami, Kilchis, Trask, and Tillamook. Sample locations at the uppermost reaches of these rivers, directly below forestry dominated areas, generally meet water quality standards.  This indicates that wildlife and other sources from the forestry dominated areas are not major contributor to the bacteria problem in the Watershed.  Bacteria data also show a strong correlation between high bacteria concentration and precipitation, mainly in the spring, summer, and fall.  The Tillamook River routinely has the highest bacterial concentrations.  However, long-term data indicates that bacteria concentrations are decreasing in the Tillamook River. While this is encouraging, it will be over a decade before standards are being met at its current rate of decrease.

One of the most positive results from the bacteria analysis is the fact the Wilson River currently meets water quality standards at all sample locations and statistically significant trends indicate that bacteria concentrations are continuing to decrease.  This decrease can be attributed to TEP's efforts to implement the CCMP, and their education and outreach efforts with farms in the watershed.  In addition, the Oregon DEQ has had a TMDL in place since 2001 and has been working on implementation projects in the watershed.

The results of this effort have also shown that there are several areas that still have a severe bacteria problem.  These locations include Mill Creek and Holden Creek in the Trask watershed, Hoquarten Slough, and Bewley Creek in the Tillamook watershed.

What are the sources of Bacteria pollution in the Tillamook Bay Watershed?

Results of the Oregon State University (OSU) DNA Marker study indicated widespread contamination from ruminants throughout the watershed and, in certain river segments, significant contamination from humans.  The amount of bacteria each source was contributing was not determined from the techniques employed in this study, but an average frequency of detection from human and ruminant sources was calculated.  The higher the detection rate, the more likely it was that the source was a major contributor to the bacteria problem. The average ruminant bacteria detection frequency was 75%, whereas frequency of detection for human sources was much lower (35%).  These average frequencies were established in the lower Tillamook Bay Watershed, an area which has bacteria concentrations above State standards.  Average frequency of detection is much higher here than in an area of low bacteria contamination.

Although the DNA Marker Study was not able to address wildlife as a whole, it was able to test all ruminant positive samples with a primer that would indicate the presence of elk DNA.  Primer testing determined that for all ruminant-positive samples, elk DNA was not present, meaning elk were not a component of the ruminant source, giving credible scientific evidence that elk were not contributing to the Watershed's bacteria problems.

This independent report concluded that "a watershed manager's best strategy for decreasing indicators of fecal pollution in this watershed is to mitigate runoff from ruminant sources".