Parasite Detected Near Lake Mead, Potentially Deadly to Dogs

National Park Service researchers find signs of Heterobilharzia americana parasite in wildlife around Lakes Mead and Mohave.

Published on Feb. 11, 2026

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Signs of a freshwater parasite that can prove fatal to dogs have been identified around Lakes Mead and Mohave, though National Park Service (NPS) researchers said the infection risk appears low based on a two-year survey. The parasite, Heterobilharzia americana, can cause canine schistosomiasis and was recently detected along the Colorado River after dogs fell ill near Blythe, California, marking a spread beyond its traditional range in the Gulf Coast and southern states.

Why it matters

The detection of the Heterobilharzia americana parasite in the Lake Mead and Lake Mohave area is concerning, as it can cause a serious and potentially fatal illness in dogs. While the risk of infection appears low based on the NPS survey, the spread of this parasite beyond its traditional range is a worrying development that requires close monitoring to protect the health of local canine populations.

The details

NPS aquatic ecologist Riley Rackliffe led a survey of 28 sites across Lakes Mead and Mohave, collecting and testing about 1,300 freshwater snails, which are the parasite's intermediate hosts, and gathering raccoon fecal samples. While the team identified three snail species capable of hosting the parasite, those snails were rare in both lakes, with concentrations observed mostly in Lake Mohave and at the Virgin River confluence with Lake Mead. No infected snails were found during the survey, but parasite eggs were detected in raccoon feces, indicating the presence of the parasite in the local wildlife.

  • In 2024, reports emerged of a dozen dogs contracting canine schistosomiasis following exposure to the Colorado River near Blythe, California.
  • In 2026, NPS researchers conducted a two-year survey of 28 sites across Lakes Mead and Mohave.

The players

Riley Rackliffe

NPS aquatic ecologist who led the survey of Lakes Mead and Mohave.

University of California, Riverside

The university that first identified the transmission of the Heterobilharzia americana parasite near Blythe, California.

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What they’re saying

“At the moment, we've never had a dog reported to us that was infected with this in the Las Vegas-Lake Mead area. That doesn't mean they've never been infected, but that suggests that probably infection rates are low, or we would have heard about it.”

— Riley Rackliffe, NPS aquatic ecologist (Nevada Current)

What’s next

Researchers will continue to monitor the situation and work with local veterinarians to identify any potential cases of canine schistosomiasis in the Lake Mead and Lake Mohave area.

The takeaway

The detection of the Heterobilharzia americana parasite in the Lake Mead and Lake Mohave region is a concerning development, as it can pose a serious threat to local dog populations. While the current risk of infection appears low, the spread of this parasite beyond its traditional range underscores the importance of ongoing surveillance and collaboration between researchers and veterinarians to protect the health and safety of pets in the area.