DIDYMO: From a Guide’s Perspective

by Brian Kozminski, True North Trout

The aromatic lilac-like fragrance of Autumn Olive softly settles among the freshly sprouted ferns along the river’s edge. It’s the end of May, and we just had a touch of summer’s heat and humidity. The weatherman on Channel 9&10 predicts cooler evenings, even a threat of frost. There is a cloud of dancing Light Hendrickson’s just a few meters above the water; I’m guessing they are looking to drop egg sacks soon. A few Lesser Mahogany and Sulphurs are taking to flight and headed for the trees. I am focusing on acrobatic trout that summersault with preciseness and enthusiasm that even Simon Cowell would find impressive.

There is a snorting buck in the woods behind me, distracting me from whether the teener browns are snacking on emergent caddis or one of the suicidal kamikaze stoneflies that seem to dive bomb from the highest altitude. The good news-bugs. There are plenty-more than enough to make me feel less concerned about the sticky algal bloom beneath my feet. There is also a sense of relief seeing smaller trout feed in the runs and seams just above what was a solid mat of “rock snot” a couple of months ago.

While floating with clients and talking to other anglers, cabin owners, and recreational river users, I have noticed one dominant fact; there is A LOT of misinformation or none at all. I am not a scientist, but fishing with Sam Day, a water quality specialist from the Tribe, I have learned what to look for and how important it is that we spread the word instead of the didymo.

Some of the unknowns, such as much of how and why it acts, are very much a mystery. Speaking with the Michigan DNR, they are at a standstill, monitoring and waiting to see how didymo works. According to Sam, the St. Mary’s River has didymo, and it acts as though it may be ‘native’ to Lake Superior, much like brown trout act native in some of our rivers, even though they were introduced as ‘exotic species.’

We don’t know why it seems to favor sections of rivers that are nutrient deficient, especially low in phosphorous. We are also uncertain why and when it spreads. Does it spread from separation? Does it bloom and flow downstream? As a guide, I’ve noticed less rock snot on the Manistee River below M66, especially where the current seems to be swifter. This could be partly due to the numerous large sandy tracts near Dutch John that may act as speed bumps. The algae need something to attach to, and sand is not a likely source. Further down the river system, it is more fragmented and almost non-existent.

Perhaps the sweepers act as seines or nets and collect the grey/white drifting rock snot. The dead algae lose some brown/ yellowish tones and become greyer as it drifts downstream. Reach in and inspect the mass of didymo; feel it and investigate the fibers. The texture of the Didymosphenia geminate is not slimy but rather much more like wet wool. This is largely due to the diatomaceous structure of the cell. When Sam and I floated after Trout Opener, we reached in and inspected some clumps, and macroinvertebrates were living in them.

There may be a change in the overall biomass of macroinvertebrates-more isopods and crustaceans were prevalent in tailwater rivers in Tennessee; less of the crawler/clinger mayflies that we anticipate in our trout rivers near the 45th parallel. I hope we don’t see a major change in the biomass we have come to appreciate.

Several cabin and property owners were surprised to learn about the spongy snotty algae that now carpeted the river bottom where they once swam and played with family. One told me the DNR said a guide with a jet boat brought it down from the Sault. Some conjecture it was a wading angler who fished the St. Mary’s for steelhead and had a trip the next day on the Upper Manistee.

The number of recreational river users in the past two years because of Covid has set this up for the perfect storm for contamination of this magnitude. We need to spread the word to canoe/kayak users and tubers who might not feel the urgency to wash and rinse their vessels before venturing to other rivers. Others have claimed to see it in years past, but why not report it? It doesn’t really matter, it is here now, and we need to regulate how much and where this goes.

“Diddy, who? Diddy what? We don’t fly fish; I don’t have to worry about it...”

On Trout Opener weekend, we noticed the usual numbers of neoprene wearing, ultra-light, worm-dunking culvert hoppers, and we stopped to chat with a few in between swinging salted minnows through deep pools. We explained the importance of cleaning fishing gear. Formula 409 has proven effective on New Zealand mud snails, while a 5% Greenworks or Dawn solution is best for preventing the spread of didymo. Thoroughly cleaning, scrubbing with a brush (like a toilet brush from the Dollar Store), rinsing, and allowing your boots, waders, nets, and gear to dry for five days before going to another river is critical.

My biggest fear is switching rivers; even while I routinely clean my boat and gear and switch out the anchor and anchor line, there is no way I can be 100% certain I can sanitize every square inch of my boat. The reality that didymo has spread to other rivers is better than 90%. It may take until later in the season to reveal how much it has spread. We may see a seasonal bloom in the Upper Manistee later in the year, like the fall. We are far from out of the woods.

Please follow these steps:

• AVOID using felt sole boots.

• CLEAN all aquatic plants, animals, and mud from watercraft/anchors before leaving the boat ramp.

• DRAIN water-related equipment (boat, ballast tanks, portable bait containers) and drain bilge and live well by removing boat plugs.

• SPRAY watercraft and equipment with a high-pressure sprayer.

• RINSE waders, hip boots, nets, and gear with hot water or wash with 5% Dawn/Greenworks or soak in Virkon S.

• DRY gear for five days.

MothBear Outfitters from Alpena has teamed up with TU selling coffee with a portion being donated to Michigan TU for additional signage and wader wash stations in Michigan. Find them at mothbear.com.