DENVER (AP)? The brown slime blanketing the rocks in Middle St. Vrain Creek looks to the casual observer like ? well, slime.
But to biologist Sarah Spaulding, the algae, officially Didymosphenia geminata, look like big trouble.
“Didymo,” aka “rock snot,” is spreading to streams across the country, growing so thick it forms mats that look like toilet paper.
“Many of the people who see didymo actually think someone has dumped raw sewage into the river,” said Spaulding, a U.S. Geological Survey researcher.
“And that’s never the case, as didymo usually occurs in what we think of as clean waters,” Spaulding said.
Didymo has been found smothering the bottoms of streams in the Western states, including Colorado, Utah, Arizona, Montana and Nevada.
It is the prime suspect in the decline of brown trout in South Dakota, where biologists think the organism has grown so thick it’s choking out the flies the fish feed upon.
“We think every angler out there should be paying attention to this one,” said Kajsa Stromberg, conservation coordinator for the Federation of Fly Fishers.
The rise of didymo is a mystery.
Species such as kudzu in the South and zebra mussels in the Great Lakes have spread and become pests because they are exotics brought into the United States from abroad.
But didymo has probably always lived in the high mountain, pristine lakes of the West. In Colorado, it was first described in the Fryingpan River in 1975.
Didymo is microscopic diatom, a once rare organism with cell walls made of silica, giving it a rough feel despite its slimy appearance.
In recent years, something has triggered the diatom to explode in numbers and in places beyond its historical range, such as Arkansas and Tennessee.
“Clearly, conditions are stacking up somehow to make this one fat, happy organism,” Spaulding said.
“At first, I thought there had been some kind of mutation, but that’s not the case,” she said.
Its discovery last year in New Zealand created a panic, leading the government to restrict access at some rivers and to consider dousing the algae in bleach or draining waterways.