The Vermont Legislature, on the recommendation of the Fish and Wildlife Department, have outlawed the use of felt-soled waders or boots in Vermont waters starting April 1, 2011.
They have done so to help curb the spread of aquatic invasive species such as whirling disease of fish and didymo, a microscopic algae more commonly known as "rock snot." Didymo (Didymosphenia geminata), although naturally present in many parts of Europe, Asia, and North America, has begun to spread into areas where it has never been before. It is now found in many western U.S. and Canadian rivers, some tailwater rivers in the south and, more recently, in Quebec and New Brunswick, as well as other locations around the world.
Historically, this diatom occurred mostly in northern latitudes in low nutrient waters; now it occurs in more nutrient-rich water and at lower latitudes. No one is quite sure why, but it is adapting and spreading. Individual cells can't be seen without a microscope but they can produce a fibrous stalk that can develop into visible mats. It covers the stream beds with a dense growth several inches thick and can form nuisance blooms. Didymo is light tan to brown in color. It clumps together and feels like wet wool. It's never slimy or slippery and the clumps are very cohesive. It resists being pulled apart.
As their stalks lengthen they form ropy strands that may attach to plant stems. They may become white in color with dead strands that dry on rocks looking like tissue, fiberglass, or toilet paper. "In some cases didymo can change aquatic insect communities and native populations in streams," says Vermont Fish and Wildlife Department fisheries biologist Shawn Good.
"The abundance of certain types of trout food like mayflies, caddis flies and stone flies have been shown, in some instances, to decline dramatically where didymo blooms are found." The spread of didymo has been of great concern to the Department since it was first found in the Connecticut River in 2007. An earlier bloom was found in the Battenkill River in New York in 2006.
Since then it has been found in the Mad, White, East Branch Passumpsic and Gihon Rivers. However, biologists around the world have been concerned about the spread of didymo for quite some time. In a symposium in Montana in May of 2006, several papers were presented on the problem. Barry Biggs from New Zealand stunned the audience with pictures taken in 2005 of the destruction of the river bottom of the Mararoa River. Although the rates of growth and biomass accumulation in the Mararoa have not been seen in other parts of the world, it was startling to see the devastation. At the same symposium Max Bothwell, Environment Canada, proposed that the spread of didymo on Vancouver Island is the result of the development of waders with felt soles and increased travel by anglers to fish geographically distant rivers.
Many participants echoed the sentiment that felt-soled waders are one of the highest risk vectors in the spread of didymo on a global scale. The Federation of Fly Fishers has joined in the battle. They have been helpful in spreading the information to their members on the problems this invasive algae can cause. Fly fishermen and other fishermen are the ones who travel in these streams. They walk the bottoms and carry the algae on their equipment when they leave the stream. It is important that all fishermen try as best they can to help in the fight. The elimination of felt-soled boots and waders is one small step to try to curb the spread. They have been found to be carriers of microscopic species that spread through cells and spores. Felt is especially problematic because it is difficult to dry, clean, or disinfect. Felt's woven fibers create voids that remain damp for long periods of time and didymo cells and other small material can penetrate and occupy these voids.
Different treatments have been found to be ineffective at disinfecting these spaces. Even rubber boots can be a problem, but far less so. These algae cannot migrate upstream. The only way they can move is as a hanger-on. This can include the boots of fishermen. If you fish at the mouth of a stream and then head upstream, you could be carrying these algae along on your equipment. It is recommended that you develop the habit of at least brushing your boots when you leave a location or perhaps even disinfecting your boots between stops with a bleach solution. The best way to prevent the spread of this material is to let your boots bake in the sun. This will kill whatever is on them. We continue to read and see the spread of exotic species and live forms around the world. The ability of a fisherman to be in a stream in Maine one week and fishing in Chile the next using the same boots and equipment provides a means by which all of these various life forms can be transported around the globe. This globalization will not stop, nor should it, but we all must be aware of the fact that we are carriers wherever we go.