A Tiny Jellyfish Relative Just Shut Down Yellowstone River

On August 12, Montana officials realized that the mountain whitefish of Yellowstone River were dying en masse. They sent corpses off for testing and got grave news in return: The fish had proliferative kidney disease—the work of a highly contagious parasite that kills between 20 and 100 percent of infected hosts. Tens of thousands of whitefish were already dead, and trout were starting to fall.