The Canadian Food Inspection Agency has found whirling disease in the North Saskatchewan River watershed.
Whirling disease can cause brain damage and deformation among juvenile fish, causing them to "whirl" in a circular pattern.
The declaration covers all streams, creeks, lakes, and rivers feeding into the North Saskatchewan River. The declaration ends at the Saskatchewan border.
The announcement came after declarations of infection in the Bow, Oldman, and Red Deer River watersheds.
Over the past year, the province has been increasing its efforts to fight whirling disease. The Government of Alberta opened a whirling disease laboratory in Vegreville last summer, and hired more staff throughout the province to increase education and prevention efforts.
The province will be working with the University of Alberta to fight the parasite.
In Alberta, various types of trout and whitefish are most vulnerable to the disease. Whirling disease does not affect human health.