ShareThisOn a sunny stretch of the Bear River near Colfax, Calif., in the Sierra foothills, the cool water carries a nasty surprise for swimmers and fishermen.
Look closely at the water flowing by. It carries clots of a feathery substance that looks like shredded toilet paper.
But this isn't sewage. About 10 miles of the Bear River below Rollins Reservoir is infested with a strange algae called "didymo," short for its scientific name, Didymosphenia geminata.
The algae's slang name describes the species better: "rock snot." Though it looks slippery, it feels more like a wet shag carpet.
"No doubt, it is pretty yucky, and that's the complaint from a lot of recreationists," said Leah Elwell, program director at the Center for Aquatic Nuisance Species in Livingston, Mont., which monitors the problem nationwide. "If you're kayaking, you don't want to get a mouthful of that. It does kind of foul up your day."
Didymo is considered native to North America. But scientists know very little about the algae, and they've grown alarmed by a mysterious change in its behavior in recent years.
So-called "nuisance blooms" of didymo, like that in the Bear River, are being reported with increasing frequency around the world. Experts suspect everything from climate change to a genetic mutation in the algae itself.
"There are a lot of unanswered questions about why things are happening the way they are now," Elwell said.
The Bear River bloom was discovered in July by fisherman David Ryland.
"This stuff covers everything for miles," Ryland said. "All the little bugs that live in it have a hard time surviving. If they don't survive, the fish don't survive, and we lose that recreational opportunity."
Those blooms also can clog water systems and hydroelectric facilities.
The algae is perplexing scientists for several reasons:
-- The blooms seem so massive not because of the algae itself, but because each cell grows a narrow stalk that can persist in the river for months after the algae dies, causing the "drifting toilet paper" effect.
-- The blooms don't seem to deprive the water of the oxygen that fish need to breathe. In fact, the algae mats themselves are "supersaturated" with oxygen, in the words of a 2007 paper that Elwell co-authored.
-- The blooms usually occur in cold, clear streams, not the polluted or stagnant waterways where algae typically explode.
-- Blooms recently were discovered in warm and degraded water also, greatly expanding the number of habitats the algae might overtake. They can occur in either shallow or deep and slow- or fast-moving water.
So troubling are the potential effects on the environment, recreation and plumbing that New Zealand recently adopted penalties of five years in prison and a $100,000 fine for anyone intentionally transporting the algae.
Didymo showed up in New Zealand in 2004, marking its first appearance in the Southern Hemisphere. It was likely transported on a vacationing fisherman's wading boots.
A movement is now afoot to ban felt-soled wading boots. Felt improves traction on slippery rocks but can trap moisture -- and viable didymo cells -- for weeks. Anglers may unwittingly transport didymo to new locations unless such boots are thoroughly cleaned and dried.
New Zealand was the first nation to ban felt-soled wading boots. Vermont was the first U.S. state to do so, Elwell said, and others plan to follow suit. But boot bans won't be enough, she said, because rivers host so many activities. For instance, boats can retain water for weeks within their hulls or plumbing systems. So can firefighting equipment.
The U.S. Environmental Protection Agency recommended in a recent flier that equipment used in rivers should be washed in a solution of 2 percent bleach or 5 percent dish detergent for at least a full minute, then thoroughly dried.
(E-mail reporter Matt Weiser at mweiser(at)sacbee.com.)
(Distributed by Scripps Howard News Service, www.scrippsnews.com.)
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