Blame it on the Fungus

The 60-mile section of the upper Clark Fork from Warm Springs to Jenns has been mostly overlooked by trout anglers in Missoula. Though technically it is the headwaters of Clark Fork, it has a reputation for long sections of low fish counts, and tough sections of fish stacked like cordwood that are just damn hard to get at. Travelers along I-90 often gaze over the Clark Fork as they come into Missoula and wonder, why no one is fishing in there when it looks so good? For years, the contamination from the extensive mining in the Butte and Anaconda region of the state put fish numbers on the Clark Fork way down.

 Recent years have seen big comebacks, thanks to the great works of conservation groups, but the warmer waters in the summer have made this section the domain of mostly brown trout, with native fish moving into the cooler waters lower in the Clark Fork for the most part. Still, the brown trout numbers have been good in recent years. 2,400 browns were found in last year’s survey by Montana Fish, Wildlife and Parks of the first two miles of the river, a very good number. Unfortunately, this year things went a little wonky. Biologists for FWP are reporting that they have only found 600 brown trout in the same section this year, a number they attribute to a funky fungus known as saprolegnia.

A brown trout afflicted with the saprolegnia fungus, a naturally occurring outbreak that might be effecting fish numbers this year on the upper Clark Fork. Photo courtesy of Montana Fish, Wildlife and Parks.

The fungus is naturally occurring, and present most years in the river. Why it shows up larger in some years than others isn’t well known. It does tend to effect the larger trout that are competing for spawning territory in the high river, and though it does mean lower numbers of the big boys, it doesn’t necessarily reflect into lower fish numbers. Last year’s water temperatures in October were higher than usual, which experts believe contributes to the growth of the fungus. Likewise, they believe this stress on the fish causes more competition for spawning habitat.

According to some experts, the lower numbers of the larger breeders means more opportunity for the smaller fish to thrive and grow themselves. This fungus, and low fish numbers have also been found on the Big Hole and the Big Horn rivers this year. Some speculate that the dewatering of the rivers by irrigators at these headwaters is contributing to the overgrowth of saprolegnia, due to rising temperatures of the rivers when water is sucked out and sprayed over crops and lawns. More fodder in the conflict between big irrigators and the outdoorsman in Montana.

Here in Missoula, we’ll see how this plays out with our fishing in the coming months, and we’ll keep praying for a wet summer. There seems to be no slowdown in the dewatering of our rivers by big agriculture, and water rights in low water years is always on the forefront of the angler’s mind. But for now, if you come home skunked from the river, you can blame it on the fungus and not that horrible cast of yours.


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