The scientific name is Didymosphenia geminata — or just didymo for short — but its more commonly used, and perhaps fitting, term is simply “rock snot”. Its presence has been confirmed in the Kootenay Lake watershed, and its unwelcome arrival has the Ministry of Forest, Lands and Natural resource operations (FLNRO) and the Fish and Wildlife Compensation (FWCP) asking anglers and other water users to take extra care in cleaning gear in an effort to slow its spread.
In early May, while monitoring the Gerrard rainbow trout spawning run at the outlet of Trout Lake, FLNRO habitat technician Terry Anderson floated over a mat of didymo covering approximately at least 400 square meters.
“We know that it is already in the Salmo and Columbia rivers,” said Anderson, “but this is the first time we have confirmed it in the Kootenay Lake watershed on such a significant scale.”
Some basic actions will help reduce the spread of didymo: avoid using felt bottoms on waders, clean all gear (waders, boats nets, etc.) between water bodies, preferably with a light bleach solution, and allow the gear to dry thoroughly.
“It only takes one cell on your gear to move didymo from one system to another,” added Anderson, “so it’s imperative that we all make an effort to slow its spread.”
Didymo is species of algae that can either be free floating or attached to rocks, gathering together to make gelatinous blobs or thick mats, thus earning its “rock snot” moniker. Under water, these mats can resemble thick shag-pile carpeting, ranging in colour from pale yellow-brown to white, and if they get washed-up on shore or the water level drops these dried mats often get confused with dried toilet paper.
“In some circumstances, thick mats of didymo can restrict water flow, and therefore affect oxygen levels in fish spawning and rearing areas,” said senior fisheries biologist James Baxter with the FWCP, a joint partnership between BC Hydro, the province of B.C., and Fisheries and Oceans Canada. “It can also cause gill irritations and, if the didymo reaches high enough concentrations, it can even displace some fish species.”
Didymo is not thought to adversely affect drinking water, except for colouration and odour. Swimmers have reported feeling itchy when downstream of heavy concentrations.
Although didymo is native to some parts of central North America and is often found in clean and unpolluted streams and rivers, it is considered an invasive species here, and its spread over the last 10 years has biologists concerned. It was first discovered in B.C. on Vancouver Island in 1989.
“One theory is that the spread of Didymo is connected with increased ultra violet light levels,” said Baxter. “There is no connection with the Kootenay Lake nutrient restoration program, given the fact that this latest discovery was made well upstream.”
If anyone sees large mats of didymo, they are asked to report them to the aquatic invasive species co-ordinator at Ministry of Environment by emailing Matthias.Herborg@gov.bc.ca. For more information on the FWCP, visit fwcp.ca.