Officials at the Dworshak National Fish Hatchery in Idaho said they had no choice but to destroy tens of thousands of juvenile steelhead after the deadly virus, Infectious Haematopoietic Necrosis, or IHN, was found in two of the hatchery's holding ponds. The virus can be carried and passed on by survivors, posing a threat not just to other holding ponds but bigger water bodies. Spokesman-Review.