PEARL  Paleoecological Environmental Assessment and Research Laboratory

Department of Biology, Queen's University, Kingston ON, Canada, K7L 3N6

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Bird Biovectors

“Rock snot” algae not invasive to salmon rivers of eastern Canada

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Collecting a sediment core. Lakes are natural archives of environmental change that occurs within their waters and surrounding landscape. Sediments accumulate chronologically at the lake bottom and can be dated using well-established techniques. Sediment cores from Lac Humqui and Lac au Saumon were collected in March of 2012 through the ice. Photo Credit: Carole-Anne Gillis

Didymo valve. Photomicrograph of the nuisance diatom Didymosphenia geminata, commonly known as didymo or “rock snot”.  Extensive blooms of didymo in dozens of relatively pristine rivers from Quebec and New Brunswick have been observed since 2006. Photo credit: Michelle Lavery

Planktonic diatom valve. Planktonic diatoms, such as this Cyclotella species, have increased over the past several decades in many lakes throughout the Northern Hemisphere in response to climate warming and associated limnological changes. Our control site, Lac Humqui, shows a striking compositional shift in diatoms beginning at ~1970. Photo credit: Kathleen Rühland

Didymo bloom. In 2013, the Duval River (tributary of the renowned Bonaventure River) experienced the most severe didymo bloom ever recorded in eastern Canada and comparable to extreme blooms observed over the past decade in New Zealand. In eastern Canada, recent climate warming may play a role in the establishment of conditions that favor didymo proliferation. Other Canadian provinces where didymo blooms have been identified as a concern include British Columbia and Alberta. Photo Credit: Michel Chouinard

Juvenile Atlantic salmon. Because of habitat overlap, didymo blooms pose an additional threat to vulnerable salmon populations and may reflect changing freshwater environments in these iconic river ecosystems of Quebec and New Brunswick. Blooms are known to impact the invertebrate prey and feeding behavior of the juvenile salmon. That said, researchers still have a relatively poor understanding of the direct impacts of didymo blooms on juvenile salmon and their habitat. Photo credit: Jonna Karhunen

Underwater perspective of a bloom. A didymo mat several centimeters thick covers the rocky substrate of the crystal clear Duval River. Thick and extensive blooms are known to affect the structure and function of river ecosystems. Didymo’s recent proliferation is likely unprecedented in eastern Canada and elsewhere around the world. Photo Credit: Carole-Anne Gillis

Didymo on rock. Although the distribution of didymo within a river ecosystem can be patchy, sections of river many kilometers in length can be almost entirely covered by didymo if conditions are favorable. Here is an example of didymo growth from the Patapedia River. In this particular stretch of river, for several kilometers, the percent coverage of didymo was >75%. Photo Credit: Michelle Lavery

Patapedia River algal survey. In August 2012, Queen’s University researchers visited several rivers in the Restigouche River watershed to conduct biomonitoring surveys to better understand the ecological distributions of didymo and other riverine diatom species. Photo Credit: Michelle Lavery


Didymo on rock. A growth of didymo covers the surface of a rock from the Upsalquitch River. Didymo has the texture of wet cotton and is sometimes referred to as “rock snot”. Photo Credit: Michelle Lavery

Patapedia River. Rivers in the Restigouche River watershed are noted for their excellent water quality and these ecosystems are considered relatively pristine. Didymo presents an interesting paradox in that blooms tend to occur when dissolved nutrients are low. Typically, algal blooms develop when excess nutrients enter a lake or river. This is known as cultural eutrophication and in extreme instances causes severe ecological damage. Likely, several factors are favouring didymo proliferation in eastern Canada, including climate warming. Photo Credit: Joshua Kurek

Restigouche River view. This region of Quebec and New Brunswick is noted for its remoteness, relatively minimal human impacts (aside from forestry operations), and a large number of world-class Atlantic salmon fishing opportunities. Renowned rivers in this region that are experiencing recent didymo blooms include the Restigouche, Matapedia, Bonaventure, and Cascapedia. Photo Credit: Joshua Kurek

Salmon pool. A salmon holding pool on the Patapedia River. Note the coverage of didymo on the rocks in the foreground. Photo Credit: Michelle Lavery


Didymo on rock. Didymo blooms several centimeters thick have been observed on the Upsalquitch River in New Brunswick. After a large rainfall event in 2013, the salmon barrier on the northwest Upsalquitch River became clogged with didymo that had been released from the substrate because of high waterflow. Photo Credit: Michelle Lavery

Atlantic salmon angler. A New Brunswick angler practicing catch-and-release of a salmon from the Patapedia River. Recreational angling for wild Atlantic salmon is important to the economy of eastern Canada and economic benefits were estimated at $255 million in 2010. Anglers often complain of clumps of didymo fouling their fishing lines and the unsightly nature of extreme blooms.  Photo credit: Nick Levandier

Patapedia River. The Patapedia River is remote and fishing is restricted to only a handful of permitted anglers each day. At access points, anglers are advised to wash their equipment in order to reduce the chance of didymo (and other aquatic species) spreading to new ecosystems. Didymo can live for days in damp fishing gear and several states in the US have instituted bans of felt-soled wading boots. However, changing river conditions may be an important factor to consider with respect to recent didymo blooms. Photo Credit: Joshua Kurek


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