Rock Snot!

A freshwater alga, Didymosphenia geminata, is spreading rapidly in streams worldwide. "Didymo" or "rock snot" as it is now commonly called, seems to thrive in upland headwaters where fish go to spawn and it also tolerates nutrient-poor waters in urban and industrial settings. Making its way to New Zealand in 2004, scenic rivers were rapidly covered with rock snot mats the likes of which scientists had seen nowhere else¹.

I think that I have often seen didymo myself here in the United States without knowing exactly what I was looking at. The didymo alga organism is a diatom with a microscopic skeleton of silica. In fact, didymo is one of the largest known diatoms and it also produces a long stalk which accounts for most of the "rock snot" mass².

Fishermen and recreational boaters have recently become aware that they may be vectors responsible for spreading didymo. According to an EPA leaflet distributed in Montana, boat hulls, lifejackets, and fishing gear (particularly waders) should all be inspected at the end of a day on the river. Because didymo can remain viable for several days if kept moist, even microscopic traces remaining on our equipment can transfer it to new waterways. This is probably how it first got to New Zealand, for example.

The recommended procedure for removing all didymo traces is to soak gear for at least one minute in a 2% solution of household bleach, or a 5% solution of dishwashing detergent or salt. A recent posting on "The Wild Life" blog of the Roanoke Times shows that at least one trout fisherman here in the United States has gotten the message and is using the bleach procedure.

¹ Velasquez-Manoff, Moises, 2007, "Mysterious alga threatens rivers," Christian Science Monitor, March 1.
²Kilroy, Cathy, 2004, A new alien diatom, Didymosphenia geminata (Lyngbye) Schmidt: its biology, distribution, effects and potential risks for New Zealand fresh waters. Christchurch: National Institute of Water and Atmospheric Research, Ltd.