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.