Scientists James Ranville, Carsten Prasse, John Spear, Noor Hamden, Carmen Villarruel, and colleagues studied how recreational activities such as whitewater rafting around Labor Day weekend 2022 affected the chemistry and microbiome of a natural stream. They presented a preliminary assessment of the chemical and microbial components at the ACS Fall 2023 meeting of the American Chemical Society. Now, the researchers have expanded their analyses of Clear Creek in Colorado to include additional organic contaminants. They took samples of the water downstream from a busy area where people were whitewater rafting and surfing and compared the results with an undisturbed site upstream and a day when no one was at either site. Their observations indicate changes in:

• Metals: People in the stream have disturbed the sediment, causing particles containing copper, lead, and zinc to become resuspended in the water.
• Microbial community: The abundance of microorganisms associated with the human gut microbiome increased in the presence of humans but reverted to an undisturbed, basal microbiome within 48 hours.
• Organic compounds: Analyses have detected a wide range of compounds, such as those from personal care products, including makeup and hair styling products, and insect repellents. Some, such as the painkiller acetaminophen, also suggest human excretion in the stream.

While high levels of swimming and runoff have had an impact on the stream, the study’s findings suggest that such human activity has had no long-term effects. However, the researchers say that native stream organisms may respond negatively to prolonged or repeated exposure to metals, human-associated microbes, or organic compounds of concern.

The authors gratefully acknowledge funding from the National Science Foundation and Johns Hopkins University.