Fly fishing: Verdict still out on Didymo’s longe-range effect

We’re a full year into the age of didymo now, and the most popular trout streams in eastern New York
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We’re a full year into the age of didymo now, and the most popular trout streams in eastern New York and New England have, at least so far, been spared devastation by the indestructible invasive algae.

What the future holds, time will tell.

Scientists in Vermont, New York and other states in the region reported the alarming news last summer:

Didymosphenia geminata had been confirmed present in the Battenkill, the White and Connecticut rivers in Vermont and the East Branch of the Delaware.

Because we anglers love to hop from river to river, gas prices be damned, no one was surprised when didymo was reported this summer in the West Branch of the Delaware, probably the best trout stream in the eastern United States. I for one will be surprised if it doesn’t show up in the rest of our big-name rivers in the months to come, despite efforts by state agencies and groups like Trout Unlimited get us to thoroughly clean and dry our waders before moving from one river to another.

Didymo has the potential to grow into long, thick, streambed-smothering mats that have been compared to brown fiberglass insulation. It loves cold, clean water, and once it’s in a stream, there’s no known way to get rid of it.

Didymo does not directly threaten fish, but it can wreak havoc on their habitat. The worst kind of bloom buries the substrate where aquatic insects live, and those insects are what keep trout alive.

It’s thought to have contributed to a marked decline in the fishing on Rapid Creek in South Dakota. And yet, didymo has been around in the Colorado Rockies for decades, and people still visit the mile-high state in large numbers to fish for trout. In a couple of spots in the Pacific northwest, it went away on its own.

In New Zealand, where huge trout challenge skilled anglers in gin-clear water, felt-soled wading shoes have been banned as of Oct. 1. Damp felt is considered the number one way didymo spores get transported from one river to another.

Norm McBride of the Department of Environmental Conservation has spotted didymo in the Downsville Covered Bridge and Airport pools on the East Branch of the Delaware and in the the West Branch, above and below Deposit. His office has posted signs at access points along the rivers in hopes that awareness of the precautions will slow the algae’s spread. And he’s alarmed at how quickly it has grown.

“The didymo growth seen in the East Branch this year above Corbett was far worse than anything I saw last year,” he said. As for its long-term impact, “we’ll just have to wait and see.”

Nonetheless, over the summer he said his office had received no complaints about the impact of didymo on the fish or the fishing.

Nor had Dale Robinson of Saratoga Springs, who crosses the Battenkill eight times on his way to work as the fishing manager at the Orvis Co. flagship store in Manchester, Vt.

“I saw a stretch last year below Route 22 in Salem where the water was low and there were areas where the slime was exposed to the air,” he said. “But I have not seen any floating dead fish. I have not heard one person tell me that ‘Hey, my favorite run that used to have lots of fish has no fish now and it’s full of rock snot.’ ”

Still, he added, “I can’t imagine it does any good.”

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