In the Upper Connecticut River and Vermont's White River, an invasive algae called didymo, aka "rock snot", has been found. If it spreads, it could wipe out wild trout populations. Didymo likes cold water and forms huge mats covering gravel and rocks on stream beds. The algae prevents benthic invertebrates from living there, and these invertebrates are the basis for the diet of young trout.
Didymo spreads really easily because the cells are tiny. They absorb into clothing and footwear and stick to hard surfaces, and can survive eight months or more on gear that is not thoroughly cleaned and dried. Using a 5% detergent solution made of dish soap or laundry detergent and hot water to soak clothing and gear for 30 minutes will kill the algae. Hard surfaces like kayaks and fishing gear should be washed in this solution as well.
New Zealand has a lot of experience with this nasty invasive. They have a great website with more information here: http://www.biosecurity.govt.nz/