Survey of Pathologic Microorganisms in the Streams Along the Tahoe Rim Trail.

Area of Science:

• Environmental microbiology
• Water quality assessment
• Public health

Background:

• The Tahoe Rim Trail (TRT) is a popular recreational area, highlighting the need to assess the safety of its water sources.
• Pathogenic microorganisms like Escherichia coli, Giardia, and Cryptosporidium pose potential health risks to humans through contaminated water.

Purpose of the Study:

• To estimate the contamination levels of key waterborne pathogens in streams along the TRT.
• To evaluate the presence and concentration of Escherichia coli, Giardia, and Cryptosporidium spp. in TRT water sources.

Main Methods:

• Water samples were collected from 6 sections of the TRT during summer and early fall 2023.
• Escherichia coli was quantified using Standard Methods 9223B.
• Giardia and Cryptosporidium spp. were detected using EPA Method 1623.

Main Results:

• Escherichia coli counts ranged from <1 to 29.2 MPN/100 mL, with no significant differences between streams or sampling times.
• Giardia was detected at counts from 0 to 7/10 L, with significant differences between the highest and lowest concentration streams.
• Cryptosporidium was found at counts from 0 to 1/10 L, with no significant differences between streams or sampling times.

Conclusions:

• Escherichia coli, Giardia, and Cryptosporidium are present in TRT streams.
• The risk of illness from occasional direct water consumption is considered low.
• Filtering or treating all backcountry water is recommended; further studies are needed for comprehensive risk assessment.