The Parasite That Killed 4,000 Whitefish in Yellowstone Has Spread To Surrounding RiversThe Parasite That Killed 4,000 Whitefish in Yellowstone Has Spread To Surrounding RiversA parasite called Proliferate Kidney Disease caused the death of an estimated 4,000 whitefish in the Yellowstone River back in August.Nick ChrestensonNick Chrestenson