A fast-spreading disease in fish is now causing greater concern for provincial and federal government officials because it’s now been found in the Bow River watershed.

Whirling disease, caused by a parasite, affects fish by causing changes to their appearance and a whirling swimming pattern.

The deformities eventually result in the death of the fish.

In the most extreme cases, the parasite has wiped out 90 percent of fish stocks in affected waters and while officials don’t believe that will happen here, they are still monitoring the situation.

For now, the Bow River in Calgary appears to be healthy.

“In some places it's thought that fish have developed a resistance over time following a whirling disease outbreak -- maybe the fish here are resistant or have some resistance to it -- we just don't know that yet, so I think that we're going to have to be really cautious over the next several years to see how this plays out," said Lesley Peterson, a biologist with Trout Unlimited.

The disease is harmless to humans but authorities want people to help prevent the spread of the illness.

Anglers, boaters and recreational water users can help stop the spread of the disease by:

  • Not moving live or dead fish from one body of water to another
  • Cleaning boats and equipment after use
  • Drying all equipment thoroughly before transporting
  • Washing and drying dogs that have swum in the river

The types of fish most commonly affected are rainbow, westslope cutthroat and brook trout, some salmon and mountain whitefish.

If you suspect a case of whirling disease, call 1-855-336-BOAT (2628).

(With files from CTV Calgary's Bill Macfarlane)