"Scientists were looking for the presence of Naegleria fowleri, a type of amoeba that is the main cause of primary amoebic meningoencephalitis (PAM). The condition has a fatality rate of 98%. Essentially, when a person goes swimming, the amoeba can enter the brain through the nose. It then causes brain swelling and the destruction of brain tissue. Death normally occurs within 1 to 7 days of infection."
gearjunkie.com
"In Yellowstone, it was present at Firehole River, Boiling River, and Lewis Lake hot springs."
I've paddled the Lewis River in Yellowstone in 2004, so this now seems more than a theoretical risk. But I didn't swim.
3 National Park Sites Test Positive for 'Brain-Eating Amoeba' in Water
A new study shows potentially dangerous concentrations of Naegleria fowleri, a 'brain-eating amoeba' in three NPS-managed areas.
gearjunkie.com
"In Yellowstone, it was present at Firehole River, Boiling River, and Lewis Lake hot springs."
I've paddled the Lewis River in Yellowstone in 2004, so this now seems more than a theoretical risk. But I didn't swim.