What Can We Do About Didymo? Help Protect Against “Rock Snot”

Walking into the Gunpowder River north of Baltimore -- one of my favorite trout rivers here in Maryland -- I was upset to find this news: didymo has invaded the river.

The problems with didymo are many. As an invasive species, didymo distinguishes itself by two traits: its astonishing ability to spread across regions, hop scotching between water bodies, and by its equally astonishing ability to completely cover river beds in a thick, wool-like coating that suppresses native species of aquatic plants and bugs and that has earned didymo its common name -- "rock snot."

Traveling primarily by waders, and by boats, didymo puts sportsmen in the uncomfortable position of being vectors of the very thing they would hope to eradicate. Though it poses no real health risks, it can significantly compromise a river's value, and thereby impact a region's economy through a reduction in fisheries, tourism and, even, hydropower. There is no known treatment.

I've been fortunate enough to live, and to fish, in areas that have not been compromised by didymo. Much of the northeast has been saved. But I fear that may not be the case for much longer. Consider this white paper released by the EPA and the Federation of Fly Fishers:

This species is expanding its geographic range in North America and the rate that nuisance blooms are reported by the public and local media are increasing, yet little scientific investigation of the phenomenon in North America has been initiated.

While didymo may be an ecological threat, the only known cure is educational. Take the case of New Zealand. After didymo was discovered there in 2004, the whole of the South Island was declared a controlled area in December of 2005, requiring all boats, fishing gear, clothing and vehicles be cleaned before entering another waterway. Biosecurity New Zealand worked with Environment Southland, AgriQuality and Fish and Game on an extensive public awareness campaign, including road signs, magazine ads, and even heavy fines. Though new cases of didymo have appeared, the general consensus -- or at least my impression -- is that the campaign has been judged a success.

There is no effort like this in the United States. Fisherman remain largely unaware of the problem, and what to do about it.

At the entry point to the Gunpowder, I was encouraged to see the sign, and the disinfection station -- one of six stations the Maryland Department of Natural Resources has set up.

But other streams don't have any signs, let alone a station to wash your boots. At two different entrances to the Pawtuxent River, another trout river about an hour's drive southwest of the Gunpowder, there was no sign to educate or warn the public.

This is a problem. Didymo travels by the uninformed. And it travels quickly. Consider that didymo has been discovered in the Batten Kill River, in Vermont; in both the East and West Branches of the Delaware River; Matapedia River and the Patapedia River, in the lower St. Lawrence, Canada; the White River, in Connecticut. This is to name only a few.

Each river, though geographically distant, is connected by a steady stream of dedicated anglers. Educate them -- a group that has proven its commitment to protecting our waterways -- and you could successfully limit the spread of didymo. That, at least, is my theory.

We can't focus simply on the rivers that are already infested. The risk of accidental infection of other rivers is too great. We should educate the public. This could be accomplished simply by hanging printed signs at different access points of rivers, warning anglers, hikers and boaters of the risks. I know I, for one, would be happy to hang a sign, if I had a .pdf provided by the DNR or the EPA. I could print them out, and hang them whenever I access a river at an official parking area that already contains other information. The low cost, and possible impact, make this a simple, worthwhile solution.

In the meantime, what can you do to stop the spread of didymo?

Here are some simple suggestions for those of you who wade the waters of the Northeast regularly.

1. Check your waders before a stream that may be infected for any clumps of algae.
2. Clean your waders, and boots, after wading in a stream. You can soak them for one minute in 2% household bleach solution, or a 5% saline solution. The water for this should be warm - at least 60 degrees.
3. Make sure to dry your clothing -- or anything else that touched the water -- for at least 48 hours. As didymo may last longer than that, however, some suggest you fish one river per week, and let your waders dry in between.

If you're interested in more material, I'd suggest these resources:

For a model of how governments can react, and for information on didymo, check out the
New Zealand Biosecurity site.

For more detailed instructions on how to clean your equiptment, click here.

For a compilation of coverage in the United States, Trout Unlimited has a great site.

For more history, and more scientific information, read this white paper, release by the EPA and the Federation of Fly Fishers.

For pictures of what this looks like, check out this site.

And for a video, check this out. It loads slowly, and isn't particularly exciting, but it drives the message home: this is nasty stuff, something we should prevent from entering our waterways.

Do you have a story about didymo? Has it impacted your local river? Do you have a proposal for how to stop it? Write in, and tell us about it.