Yes, that's what it is - "rock snot". That is the slang name for the alga (diatom) Didymosphenia geminata, aka "didymo", or the more descriptive term, "rock snot", that is threatening aquatic ecosystems and fouling intakes.
The Christian Science Monitor (1 March 2007) had an excellent article on didymo, from where I got the information for this post. Take a look at:
www.csmonitor.com/2007/0301/p13s01-sten.html
It first appeared in the streams around Vancouver, BC, in the early 1980s and has now appeared in the Ozarks, Rockies, Iceland, Quebec, and Europe. In 2002 it appeared in South Dakota's Rapid Creek, causing a near-collapse of that stream's brown trout fishery. It recently jumped (2004) to the Southern Hemisphere, appearing in streams of New Zealand's South Island, where it is not native. It blooms in large rug-like mats that can foul infrastructure and disrupt the aquatic food web. When dry and dead, it actually looks like toilet paper.
What is puzzling is that the diatom is native to many of the streams it has "invaded". This leads to the oxymoronic description "endemic invasive species". It could be that the alga has mutated into a "superstrain". And although it is thought to be native to cold, nutrient-poor streams, it is now appearing in warm, nutrient-rich streams.
So how did it spread to New Zealand? Perhaps by globe-trotting anglers? In New Zealand, didymo has so far been kept off the North Island by a careful educational program aimed at anglers and watersports enthusiasts - disinfect your clothing and gear. Analysis of Vancouver data indicates that it may have been spread by anglers there as well. One particular culprit may be felt-soled boots, which remain wet for some time after immersion and can harbor freshwater organisms.
For precautions, see: www.biosecurity.govt.nz/didymo and www.protectyourwaters.net
So, to zebra and quagga mussels, we can add "rock snot".
And speaking of quagga mussels, they have jumped from the USA Midwest to Lake Mead in the USA Southwest. Read all about it the 5 March 2007 issue of the High Country News (www.hcn.org):
www.hcn.org/servlets/hcn.Article?article_id=16861
"Eternal boredom is the price of constant vigilance."
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