Tuolumne County Profile - Community Indicators Project 2008
Tuolumne County Profile Introduction Health and Safety Education and the Arts Natural Resources and Recreation Economy and Infrastructure Appendices Conclusion Acknowledgements

Watershed Quality

Why is this important?

High quality water in the region’s watersheds is critical for ecosystem health, and for public use and enjoyment of local water bodies. Low quality water in streams and lakes result in reduced fish and wildlife populations, increased algal blooms and drinking water treatment costs, as well as sediment related problems including flooding and loss of carrying and storage capacity in the local streams and lakes.

What is the measure?

Watershed water quality is measured by sampling local creeks and lakes for levels of turbidity, and chemical and biological contaminants such as fecal coliform bacteria colonies.

The current United States Environmental Protection Agency (EPA) recommendations for fecal coliform bacteria colonies are:

  • body-contact recreation - fewer than 200 colonies/100 ml
  • fishing and boating - fewer than 1000 colonies/100 ml
  • domestic water supply for treatment - fewer than 2000 colonies/100 ml
  • drinking water standard - less than 1 colony/ 100 ml

How are we doing?

The water quality in the ditches, lakes and streams located upstream of populated areas of the county is generally contaminant-free and of very high quality. However, as the water flows downhill through the populated areas, fecal coliform and turbidity levels of these water sources increase significantly. Identified sources of fecal coliform include failing septic systems, urban storm water runoff, agricultural livestock operations, and wildlife.

Based on available data and USEPA recommendations, the following sampled creeks may be unsafe for:

  • Body-Contact Recreation — Groveland Creek (not shown in chart), Sullivan Creek, Woods Creek, Curtis Creek, Turnback Creek, Mormon Creek
  • Fishing and Boating — Groveland Creek, (not shown in chart), Sullivan Creek, Woods Creek, Curtis Creek, Turnback Creek
  • Domestic Water Supply (even after treatment) — Woods Creek


Source(s): Tuolumne County Water Quality Plan; Foothill Watershed Assessment, http://www.tcrcd.org/index_files/Page284.htm.

Note: The water quality was measured at specific sampling sites. Not all County creeks, streams, lakes or rivers were sampled, nor was the entire length of the body of water measured.

Mountain River

Community Indicators Project
Tuolumne County - Central Sierra Mountains