The didymo dilemma


Didymo (Didymosphenia geminata), or rock snot as it is commonly known, has been found in several New York waters: both branches and the Main Stem of the Delaware River, Esopus Creek, Battenkill River, Kaydeross Creek and Roundout Creek, below Rondout Reservoir. Despite all the rhetoric, and to the best of my knowledge, didymo never became a major problem in New York State’s rivers, neither from a fishing nor environmental standpoint. In those rivers, periods of high-stream discharge flushed it away, so it never developed to a harmful degree.

When the first outcry about this nasty algae began several years ago, it was promoted in the media and believed by some prominent fly-fishing organizations that didymo spores where being transported from river to river by felt-soled wading shoes. The theory was that didymo spores were survived in the wet, contaminated soles and released into a waterway the next time the wading shoes were used. So ingrained was the belief that felt soles were a major carrier of didymo spores, that several states and even Yellowstone Park banned the use of felt-soled wading shoes. Fortunately, cooler heads prevailed in New York State and the Department of Environmental Conservation (DEC) did not ban the use of felt-soled wading shoes. Those of us who have waded and fished in extremely slippery river-bottom environments, like the Esopus creek, are very grateful for that decision.

However, the DEC does recommend that anglers using felt-soled wading shoes, expose them to a bleach solution or a product like “Spray Nine” after use—the theory being that spores of any invasive species would be neutralized by the treatment.

As a result of all the negative publicity about didymo, several large and prominent manufactures of wading equipment, including Simms, stopped making felt-soled wading shoes. Instead, they began making, marketing and selling wading shoes with soles made from non-porous, felt substitutes. Of course, the new material was promoted as being as good as or better than felt as far as wading traction was concerned. Believe me, that is not the case. I know several people who tried tried the substitute material and said it just does not work anywhere as well as the felt soles.

Now that considerable time has passed since didymo became a major issue in regard to its potential impact on U.S. rivers, what have we learned? In recent years, scientists studying the origins and spread of didymo have conducted a considerable amount of research. On July 22, “Scientific American” published an article, “‘Rock Snot’ Has Been Native to Much of the World for Thousands of Years,” that debunks the evidence that didymo is spread by felt-soled wading apparatus:

“… New research suggests this type of algae, didymo, is a native species, but the environmental conditions that triggered its visible growth in rivers, were previously rare, or absent.” The article stated that climate change could be a factor, contributing to the species’ appearance in recent years. Further, three Canadian researchers, Bothwell, Taylor and Kilroy, found that didymo is most likely to be found in rivers with low concentrations of dissolved phosphorus. In other words, the purer the water, the more likely didymo will be a problem. In rivers with ideal environmental conditions, like some in New Zealand and Chile, didymo has blanketed the river bottom, compromising aquatic-insect communities. While much of New York’s river water is pretty pure, it is not so pure that it promotes major blooms of didymo.


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