Rock Snot Invades World's Rivers

Rock snot needs a stable, rocky bottom and a freshwater flow to thrive.

A slimy yellow-brown freshwater algae that once was native to only a few small stretches of rivers on Canada’s Vancouver Island has inexplicable begun to spread to new habitats around the world.

Rock snot, or didymo, has now reached the waters of New Zealand, Iceland, Alberta and Atlantic Canada.

Starting around 1990, it underwent large blooms that caused it to spread across Vancouver Island. In subsequent years, it started to spread around the world, according to aquatic invasive species expert Matthias Herborg.

While it appears to be more of an aesthetic issue than a human health or wildlife problem, marine biologists are concerned it could alter food webs in rivers.

When dried, didymo has the appearance of soiled toilet paper, causing some to think there’s a sewage problem in the river.

"It greatly degrades the recreational experience," Herborg told Canadian Press.

Experts believe it’s spread by recreational fishermen on the soles of their felt-bottom waders. At least one manufacturer has begun to phase them out, while some U.S. states have banned their use.

Photo: University of California - Riverside