The big question at Montana streams this summer: How many trout has the deadly whirling disease killed?
The disease, caused by a microbe (Myzobolus cerebralis) transmitted to trout when they ingest infected tubifex worms, is spreading fast. Despite early findings, it’s infecting brown and brook trout and cutthroat, as well as rainbows. It could eventually infect young steelhead and salmon in the Columbia and Snake rivers.
Montana biologists know the disease has killed trout in the Swan River, a Flathead River tributary, which is a Columbia tributary.
Since the disease seems to affect only young trout, anglers probably won’t notice much of a difference in the fishing they experienced last year in streams where the disease is just starting.
Montana biologists have documented the disease in the Clark Fork below Milltown Dam near Missoula, Flint and Racetrack creeks, which are Clark Fork tributaries, and Georgetown Lake. Almost certainly the disease will spread, or has already spread, to the Blackfoot and Bitterroot rivers and Rock Creek.
But the disease is young in these rivers, as well as in the Missouri River below Holter Dam. Fishing should be status quo there this year, and possibly for years to come.
Some hope lies in research that has found no trace of the disease in tributaries to some of Montana’s infected fisheries. Biologists are hoping that trout eventually will develop an immunity to the whirling disease.