The white sturgeon iridovirus (WSIV) was detected in cultured white sturgeon Acipenser transmontanus from the lower Columbia River in Oregon, the Snake River in southern Idaho and the Kootenai River in northern Idaho, USA. In Oregon, WSIV was consistently detected in young sturgeon that were progeny from Columbia River adults and cultured in river water but not detected in sturgeon cultured in well water. In Idaho, WSIV was detected in sturgeon that were progeny from wild Snake River and Kootenai River adults after being subjected to stressful conditions of low spring water flows and high fish densities. When densities were reduced and water flows increased, mortality subsided. These observations suggest that WSIV may occur in wild sturgeon and that the virus may be present in many Northwest populations due to the long life span of the species, migratory patterns, and continuity of the river systems. Additionally, since the disease appears size(age)-specific and stress-mediated, fish culture management strategies could be used to avoid or minimize epizootics. These include iodophor disinfection of eggs, sustaining low fish densities and loadings, maintaining virus-free water supplies, minimizing adverse environmental conditions, and reducing the handling of sturgeon younger than 1 year.