Publication Summary

The Thurston County Health Department and the Squaxin Island Tribe have documented an ongoing pattern of high summertime bacteria levels in many South Puget Sound streams. A project was undertaken to identify and analyze environmental conditions in streams with high bacteria levels during the summer months.

In addition, an annotated bibliography was assembled which reviewed other studies looking at the correlation between bacteria levels and other environmental parameters. This study found a need for additional information to be collected before any in-depth analysis of a correlation between bacteria levels and other environmental parameters in South Puget Sound streams can be produced.

Data from Thurston County Environmental Health and the Squaxin Island Tribe document an ongoing summertime pattern of high bacteria concentrations in many South Puget Sound streams. Typically during the summer, elevated bacteria levels can follow two patterns: triggered by runoff or occurring during low streamflow. Summer low streamflow bacteria patterns can suggest a direct discharge that requires further investigation to identify.

Local governments have been unable to address these bacteria problems without better information about what is causing high summer bacteria levels. In 2008, a project was undertaken by the Department of Ecology to study a set of stream bacteria data. This project was requested by Thurston County Environmental Health, the Squaxin Island Tribe, and Ecology′s Water Quality Program, Southwest Regional Office.

The project goal was to identify and analyze streams with high bacteria levels during the summer.

Bacteria data were compiled from streams in five counties: Pierce, Thurston, Mason, Kitsap, and Jefferson. Data results were limited to bacteria concentrations measured from May through September, 1999 to 2007. A GIS map was produced documenting the stream location of bacteria levels above 100 cfu or 100 mpn.

In addition, an annotated bibliography was assembled which highlighted other studies looking at the correlation between bacteria and other parameters such as stream discharge, temperature, and precipitation.

Based on the literature review summarized in the annotated bibliography, it is important to consider timing and location in the collection of the bacteria samples. Also, because of the yearly variability which can occur in bacteria levels, documenting the environmental conditions (e.g., stream discharge, temperature) during the time of sampling is critical to understanding bacteria patterns.