Fly Fishers Spread Invasive Microorganisms One Step at a Time

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"If the shoe fits," the old saying goes, but for fly fishers—who prize clean, healthy, rivers and the trout that inhabit them—hearing that their boots may be responsible for spreading a virulent microorganism across the country and around the world is a difficult to accept.Didymosphenia geminata, a single-celled organism better known as didymo—and sometimes "rock snot"—was first discovered in British Columbia in 1989. Once it has established itself in a river, it proliferates quickly, forming thick mats that choke out plants and insects, removing essential food sources for the ecosystem.

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Since its discovery, didymo has spread, eventually making its way into the middle of the United States and, by 2008, Vermont. Didymo has also jumped overseas, infecting rivers in New Zealand.

Now, mounting evidence points to felt soles as a common vector for the organisms' rapid spread and governments are mobilizing to limit their use.

For fly fishers, the situation is not as simple as buying a new pair of boots. Felt soles are far superior—and safer—than rubber alternatives. Arvey McFarland, a fly fisher from Utah, told The New York Times:

In all these years, the number of times I've fallen wearing felt soles, I can count them on one hand...when I've tried various rubber and pleated soles, I've opened my right elbow and dislocated my shoulder. No more for me.

Unfortunately, the felt soles are also an ideal means of transporting microorganisms.

Jack Williams, an invasive species expert from Tout Unlimited, explained:

If you were trying to design a material to transport microscopic material around...felt on the bottom of someone's boots in a stream would be as close to perfection as you could find.

Regardless of preference, fishers may soon have no other choice than to make the switch. Already, Alaska and Vermont have banned felt-soled boots and Maryland is considering doing the same. In New Zealand, the soles are banned throughout the country.

Meanwhile, manufacturers and retailers have begun to recognize the problem as well. Orvis, a popular source of fly fishing equipment, has changed their product line from featuring 80 percent felt-soled boots two years ago, to featuring 80 percent rubber-soled boots today.

Still, while switching from felt soles to rubber may slow the spread of didymo, it is not a "magic bullet." There are likely other causes for the spread, researchers acknowledge, but eliminating felt soles may buy them precious time to find a more durable solution to the problem.