The alga, Didymosphenia geminata, commonly referred to as "didymo", is a freshwater microscopic diatom. It is found in streams and rivers across much of North America. Didymo attaches to the streambed by a stalk and it forms thick mats that can alter aquatic ecosystems. These mats have a rough texture similar to wet wool and can look like strands of toilet paper.

In recent years, streams in New Zealand, North America, Europe, South America and Asia have noted unprecedented masses of "didymo". This diatom is able to blanket up to 100% of stream surfaces by with thicknesses of greater than 8 inches, potentially altering physical and biological conditions within streams.

Why didymo? Contrary to other algae species, didymo represents an interesting paradox where didymo mats form under very low nutrient conditions. Also, managers continue to grapple with how best to address this species when faced with extraordinary mat formations. As the scientific community continues to research important aspects of didymo, we will share the latest research to help inform thoughtful management decisions.

Prevent the Spread of Didymo

Cleaning equipment between uses on different freshwater systems is important to prevent the spread of didymo and other invasive species. If you can follow the simple Inspect, Clean and Dry steps, then you will do a world of good.

For decontamination methods specific to didymo, you can learn more from the links below in the report "Decontaminating Equipment". For more information on general cleaning practices, go to cleanangling.org

General Web Resources

2013 International Didymo Conference
» Held March 2013 with professionsal in attendence from around the world. Browse the Conference Results

Region 8 of the Environmental Protection Agency
» Provides some helpful documents and field guide to understand didymo.

Biosecurity New Zealand
» This governmental agency of New Zealand provides a wealth of resources on didymo. There are many research reports, photos, cleaning information and more.

The USDA National Invasive Species Information Center
» Offers good basic profile information as well as a variety of resources from state and federal agencies on didymo.

The Global Invasive Species Database
» More basic information about the alga.

Algae Base
» Complete online source for algae, including didymo.

Recent Scientific Publications and New Information

Check back with us periodically as we update this area with the most current publications.

The Didymo story: the role of low dissolved phosphorus in the formation of Didymosphenia geminata blooms
» A scientific paper that explores the formation of didymo blooms (2014).

Exploring the environmental context of recent Didymosphenia geminata proliferation in Gaspesie, Quebec, using paleolimnology
» A scientific paper providing information on substrate conditions and didymo colonization success (2014).

The influence of light, stream gradient, and iron on Didymosphenia geminata bloom development in the Black Hills, South Dakota
» A scientific exploration of a South Dakota river affect by mat-forming didymo (2014).

The first record of invasive diatom Didymosphenia geminata (Lyngbye) Schmidt in a Patagonia Andean river of Argentina
» A scientific paper on a novel discovery in South America (2013).