Highly aggressive Rock Snot algae is invading Bear River

By: J.D. Richey
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Oh no, it’s Didymo! Yikes! As if all the invasive stuff we have here like zebra mussels, Quagga mussels, Brazilian Waterweed, Asian carp and mitten crabs, etc. weren’t enough now there’s this… It’s recently come to my attention that the destructive algae, Didymosphenia geminata, also known as “Didymo” or “Rock Snot” has invaded one of our beloved foothill trout streams: The Bear River. Didymo is a very aggressive algae that can cover entire streambeds with mats as thick as eight inches. If a large bloom occurs on the Bear, it can lead to total destruction of the fishery. Basically this stuff will smother everything in the water – it starts with a decline in aquatic invertebrates like caddisflies, stoneflies, and mayflies and other larval insects, which, in turn means there’s less stuff for the trout to eat. Over time, the food chain gets totally choked out. Too see the devastating effects Didymo, look no further than New Zealand, where it was first discovered in Lower Waiau River in 2004 and has since spread to several South Island streams, where it has wreaked total destruction on what used to be world class trout fisheries. Rock Snot looks kinda like fiberglass or wet toilet tissue and is generally brown, tan or yellow in color and, surprisingly, is not slimy to the touch. Instead, it feels kinda like wool or cotton candy. Apparently, there’s not a whole heck of a lot we can do once this junk gets into a waterway – except try to avoid transplanting it to another one. The best way to keep Didymo in its place is to avoid using felt-soled wading boots. The algae can live a long time in the wet felt – long enough for you to potentially contaminate another stream the next time you put your boots on. Luckily, many boot manufacturers are now producing feltless wading boots. You can see a review of a pair made by Simms that I did on my website at Just type “Simms wading boot into the search field at the top right). Additionally, there are several steps you can take to help avoid the spread of this invasive algae. For waders and wadingboots: To kill Rock Snot, soak waders for at last a half an hour in hot dishwater. You can do the same with your boots or the other option is to freeze them overnight (until solid). All rods, reels, fishing lines, flies, tackle boxes, nets, clothing and other equipment should be thoroughly soaked in a decontamination solution as well. You may also dry everything for at least 48 hours but items must be completely dry to the touch, inside and out, and then left dry for at least another 48 hours before entering a different waterway. If you do not want to go through all this, you can dedicate gear to a particular waterway. In other words, use the waders, rods and tackle that you fish with on the Bear River for only that stream. To learn more about Didymo, check out the blog of Ken Davis of Creekman Wildlife Survey and Photo Service (