Thank you for visiting the New Hampshire Fish and Game Department website. NH Fish and Game



Aquatic Nuisance Species in New Hampshire: Didymo or "Rock Snot"

New Hampshire anglers and boaters: be on the lookout for a new invader! The aquatic nuisance algae known commonly as "Didymo" or "rock snot" has invaded the northern reaches of the Connecticut River, marking the first official report of Didymosphenia geminata in the northeastern U.S.


This diatom species already affects freshwater rivers and streams in other parts of the U.S., Canada (including Quebec province) and New Zealand. It is not known at this time how Didymo will affect water quality, aquatic habitat and fish populations in New Hampshire. NH Fish and Game and the NH Department of Environmental Services are monitoring the situation closely and working to stop its spread to other waterbodies in the state.


It is critical for anglers and boaters to be aware that Didymo is on the move and is easily spread by even just one cell of the alga breaking off and drifting downstream in infested reaches. It is also very easily spread by waders, fishing gear and other gear that touches the bottoms of streams in infested areas, so it is essential to check and clean your fishing gear to prevent the spread of Didymo and protect New Hampshire's waters.


Anglers and Boaters: How to Clean Your Gear


Prevent the spread of Didymo by cleaning all equipment before moving from one location to another, even on the same river. If you see Didymo in New Hampshire, contact Amy Smagula at the NH Department of Environmental Services at (603) 271-2248.


CHECK: Remove everything that sticks to fishing gear, boats and trailers. Remove all visible clumps of algae and plant material from fishing gear, waders, clothing, water shoes and sandals, canoes and kayaks, and anything else that has been in the water. It takes a number of cells present before Didymo is visible to the human eye, so cleaning is also very important.


CLEAN: Use HOT tap water and lots of soap (a good squirt of dishwashing detergent). Scrub boats and other “hard” items thoroughly; scrub all gear at least one minute. Soak clothes, felt-sole waders and other “soft” items for 30 minutes!!


Be on the lookout for Didymo! If you see it in New Hampshire, contact Amy Smagula at the NH Department of Environmental Services at (603) 271-2248 or email: