Lake Mead near Hoover Dam in Nevada (Supavadee butradee/shutterstock.com) Naegleria fowleri — the single-celled organism that causes a brain infection with a 98% fatality rate — has been showing up in warm waters at Yellowstone, Grand Teton, Olympic, Lake Mead, and Newberry National Volcanic Monument, according to a SFGATE report by Sam Hill . Roughly a third of the 185 water samples that USGS biologists pulled from 40 sites tested positive. The amoeba thrives above 86°F and multiplies fast in extreme heat, which is why it has historically been a southern problem. The study authors note that PAM cases — primary amebic meningoencephalitis, the disease the amoeba causes — have been creeping north since 1962, and they expect that creep to continue as the planet warms. The CDC counted 167 cases in the U.S. between 1962 and 2024. Four people survived.…