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New Hampshire Department of Environmental Services

Didymo (A.k.A. Rock Snot)
Click to view enlarged photo of didymo Click to view enlarged photo of didymo
Click to view enlarged photo of didymo

Click on each of the images above to view enlarged photo of didymo

How to tell if you may be seeing Didymo

Location mostly clear flowing water with rocky bottom, may be attached to plants deep silty areas with no rocks or plants, highly colored waters.
Color tan, light brown or whitish green or dark brown/black
clear or transparent
Texture clumps or ropy strands, rough cottony feel, fibrous thin layers, slippery or gelatinous
Appearance no leaves or roots (BUT may attach to leaves or stems). Sometimes mistaken for fiberglass, toilet paper or tissue. has leaves or roots
looks like an aquatic plant

If your sample matches three of the "yes" descriptions above, you may have found Didymo. We’d like to know!

Please send a dime-sized sample in small container or folded in a business card to:

Samples from Vermont
Didymo identification, Water Quality Division
103 S. Main St., Bldg 10N, First Floor
Waterbury VT 05671-0408
(802) 241 – 3770 or 241 – 3777

Samples from New Hampshire
NHDES Limnology Center
29 Hazen Drive
Concord, NH 03301
(603) 271-2248 or (603) 271-3414

Be sure to include your name, address and phone or e-mail so that we may contact you.
Also, please provide a detailed description of where you found your sample: name of the river or stream, the town, and precise location (such as GPS coordinates, nearest road, or a clearly marked map).

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

copyright 2017. State of New Hampshire