The entire Bow River Watershed has been infected with whirling disease, the Canadian Food Inspection Agency (CFIA) has declared, prompting new province-wide measures to try to contain the spread.

The disease can cause infected fish — predominantly trout and whitefish — to swim in a whirling pattern and die prematurely.

The agency has also declared the rest of the province a "buffer zone" for the disease. 

Inside the buffer zone, provincial acquaculture facilities and Class A fish farms will have to test fish for whirling disease.

They will also have to implement "approved biosecurity protocols" in order to obtain a permit from the agency to stock fish from the infected area — which includes all streams, creeks, lakes and rivers that feed into the Bow River. 

Whirling disease

This map shows the area of Alberta declared infected with whirling disease. (CFIA)

Last August, the first case of whirling disease was confirmed in Banff's Johnson Lake. Since then, cases of the disease have been detected at a number of additional locations in the Bow River in southern Alberta.

The spread of the disease has led to quarantines for commercial fish operations and wreaked havoc on owners who make a living cultivating fish. 

The CFIA says its declaration does not currently affect fishing in the Bow River, and that there are no health concerns for people who use the bodies of water that contain whirling disease — or for those who eat fish that have contracted the disease.

There is no treatment available for whirling disease. Rather, the CFIA says it is focused on containment and prevention.