Whirling disease

Whirling disease is a disease of salmonid fish that has infected some trout and whitefish populations in Alberta.

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Whirling disease


Whirling disease is caused by Myxobolus cerebralis, a microscopic parasite that affects salmonid fish such as trout, salmon and whitefish. The parasite has a complex lifecycle that requires a salmonid fish and an aquatic-worm, Tubifex tubifex, as hosts.

Species such as rainbow trout, cutthroat trout and whitefish are particularly susceptible to whirling disease, though disease impacts differ among salmonid fish species and in different waterbodies.

The severity of whirling disease depends largely on the age and size of the salmonid host. Young fish are most vulnerable, with mortality rates reaching up to 90%.

Signs of infection

Fish infected with whirling disease may show the following signs:

  • A 'whirling' swimming behaviour may be observed as the parasite invades cartilage and impairs the nervous system.
  • Changes in physical appearance, including (but not limited to):
    • skeletal deformities of the body or head. This occurs when the cartilage of the spine or head is infected at a young age. The tail may be crooked and head cartilage sunken to show a sloped head.
    • colour changes due to nerve compression, so that the tail may appear dark or even black.
A comparison of a healthy rainbow trout and a rainbow trout exhibiting whirling disease symptoms
A comparison of a healthy rainbow trout (top) and a rainbow trout exhibiting whirling disease symptoms (bottom). Both fish were captured from the Crowsnest River in Alberta.

Whirling disease is not harmful to humans or other mammals.

If you suspect you witnessed a fish with whirling disease, email [email protected].

We ask that you do not disturb or remove any suspected fish – if possible, a photo, location, date, time and a few notes about what you saw (that is, species, abnormalities, how many fish you saw) will help us better direct our surveillance program efforts.

Quick facts

Learn more about whirling disease:

Whirling disease in Alberta

Whirling disease has been declared in 4 major watersheds in central and southern Alberta:

  • Bow River
  • North Saskatchewan River
  • Oldman River
  • Red Deer River

View the maps of where whirling disease has been detected in Alberta:


  • 2019

    October 3: Fish collected by the Alberta government from the Athabasca River drainage basin are confirmed negative by the Canadian Food Inspection Agency (CFIA).

  • 2018

    December 3: Several worm samples (non-Tubifex) collected from the Athabasca River watershed and one worm sample (non-Tubifex) from the Peace River watershed test positive for whirling disease, prompting the requirement for further fish sampling for 2019 from CFIA.

    August 29: Alberta government staff detected clinical signs of whirling disease in rainbow trout and mountain whitefish populations in the Crowsnest River.

    March 9: The CFIA declares the North Saskatchewan River watershed infected with whirling disease.

  • 2017

    September 16: Mount Royal University staff and students observed clinical signs of whirling disease in brown trout in several fish collected from Dogpound Creek.

    June 23: The CFIA declares the Red Deer River watershed infected with whirling disease.

    May 1: The CFIA declares the Oldman River watershed infected with whirling disease.

    February 10: The CFIA declares the Bow River watershed infected with whirling disease.

  • 2016

    August 23: Testing conducted by the CFIA confirms the presence of whirling disease from fish collected in Johnson Lake in Banff National Park.

    August 11: The Alberta government was advised of the possible presence of whirling disease in Banff National Park. Alberta Support and Emergency Response Team (ASERT) implemented the Aquatic Invasive Species Early Detection and Rapid Response Plan for Alberta. Alberta government fish biologists were requisitioned to collect fish samples throughout Alberta to test for whirling disease.

  • 1990s

    Whirling disease is first detected outside of hatcheries in streams in the United States, particularly in the intermountain west, including Utah, Idaho, Colorado and Montana. In Montana and Colorado, it was detected in depleted wild rainbow trout populations.

  • 1960s

    Whirling disease is found mostly in fish hatcheries in the northeastern United States.

  • 1950s

    Whirling disease is first observed in the United States.

Responses to whirling disease

The Alberta government and the CFIA are developing long-term detection and surveillance plans to protect Alberta’s trout and whitefish fisheries as much as possible.

Additionally, the Whirling Disease Program provides annual reports highlighting the program year and the priorities for the upcoming year.

Fish quarantine

In 2016, the Alberta government issued Ministerial Order 52/2016: Fish Quarantine Order to quarantine all commercial fish culture operations until individual fish farms and hatcheries licensed for salmonids are tested for the presence of whirling disease.

The precautionary quarantine of fish farms and hatcheries reduces the risk of whirling disease transmission from fish farms and hatcheries to wild populations, and helps protect Alberta’s fish populations and world-renowned fishing industry.

The quarantine will be in place until each facility has tested negative free of for whirling disease. Fish farms may resume stocking once they are confirmed to be free of the disease.

Temperature Monitoring Project

In 2018, the Whirling Disease Program initiated a large-scale stream temperature monitoring project to assess water temperature conditions associated with the presence of the parasite in Alberta. Whirling disease staff installed temperature loggers throughout the eastern slopes region of Alberta, ranging from the Athabasca River watershed to the South Saskatchewan River watershed in 2018. The Whirling Disease Program partnered with Trout Unlimited Canada, Canadian Conservation Corps (in association with Alberta Parks), Paul Band First Nations, and internal regional programs to install temperature loggers.

Susceptibility Study

In 2018/2019, mountain whitefish, brook trout and brown trout fry were reared from wild populations within Alberta in order to determine their susceptibility to whirling disease. In collaboration with the University of Alberta, fry were challenged with known quantities of the whirling disease parasite and the results indicated that all 3 species had increased mortality compared to fish that were uninfected. Mountain whitefish had the highest mortality (4.8 times higher than uninfected fish), followed by brown trout (4.1 times) and brook trout (1.8 times). Future testing is planned for other Albertan species including rainbow trout, cutthroat trout, arctic grayling and bull trout.

Crowsnest River Project

In 2019, Alberta government staff conducted a sentinel cage study to determine the extent and impacts of whirling disease within the Crowsnest River. Several cages, containing uninfected rainbow trout, were installed on the Crowsnest and Oldman River. These fish were tested to determine the severity of whirling disease in the river.

Decontamination Protocol

The Government of Alberta has developed a Decontamination Protocol for Watercraft and Equipment. If you participate in water-based outdoor recreation such as angling or boating, or you work around waterbodies, you can help prevent the spread of whirling disease. To review the protocol and its support documents, see the Stop the spread of whirling disease page.

Additional information

Learn more about how you can prevent the spread of whirling disease:


Connect with the Whirling Disease Program:

Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 1-855-336-BOAT (2628)
Toll free: 310-0000 before the number (in Alberta)
Email: [email protected]