San Lorenzo River Pathogens

The San Lorenzo River is cleaner than you might think.

The lower San Lorenzo River meets water quality standards for non-contact recreation for activities like paddling. The upper San Lorenzo River meets water quality standards for contact recreation, including swimming, allowing visitors to take a dip in favorite swimming holes such as the Garden of Eden and Junction Park.

Because of the continuous work of the City and County of Santa Cruz, nonprofits and the community, the river has seen improving water quality. But it could be even cleaner. The San Lorenzo River is listed on California’s “303(d)” Impaired Water Bodies, the EPA’s list of waterways that do not support human uses, like agricultural or recreational use.

One water quality standard it is considered “impaired” for is pathogens, or disease causing microorganisms, virus or bacteria. Epidemiologists recognize one type of pathogen – fecal indicator bacteria from humans – as posing high threats to public health when found at certain levels. However, while traditional tests indicate the presence of such bacteria, they cannot help to determine the origin of bacteria found in rivers and creeks. In other words, the traditional fecal indicator bacteria tests do not tell us whether the bacteria found is coming from horses, or birds, or dogs, or raccoons, or cattle or humans. This is important for two reasons:

  1. Human sourced bacteria has a higher potential to make us sick and
  2. When we know where the bacteria is coming from, we can take effective action to reduce or prevent harmful bacteria from entering the waterway.

CWC convened water quality experts in 2013 to form the San Lorenzo River Alliance’s Water Quality Working Group. In 2014, the working group, which includes the CWC, the City and County of Santa Cruz, Surfrider Foundation and Central Coast Regional Water Quality Control Board, launched a study to test for specific human waste and sewage-associated chemical and microbiological constituents. Laboratory tests for different types of bacteria, caffeine, human DNA and fecal matter indicators were run on samples from the lower San Lorenzo River and Branciforte and Carbonera Creeks. Multiple tests indicated that the source of much of the bacteria in the lower San Lorenzo River was coming from bird populations and demonstrated very little evidence of human sourced bacteria.

This initial 2014 study was conducted after a year of drought. The group is repeating this study in 2016 after a more normal rainfall year. Continued monitoring will examine how fluctuations in hydrological conditions affect bacteria levels and sources and will help CWC and partners refine the best management practices (BMPs) to be implemented to address those sources.

The working group’s ongoing efforts include source identification and control and reduction of bacterial contaminants, with an emphasis on human and other anthropogenic sources that are deemed controllable. The goal is to reduce human bacteria inputs to the lowest levels possible