Didymo Invasive Species
In North America, D. geminata is expanding its geographical range and forming massive growths in streams. This nuisance organism grows attached in streambeds and may impact freshwater fish, aquatic plants, and aquatic insects.
Didymo impacts other stream organisms, and impacts are greater when large masses are present.
Economic impacts include fouling of water intakes and a potential link to decline in fisheries. Impacts to aesthetics are common and recreationalists report unsightly masses that appear like strands of toilet paper or fiberglass. The growths become snagged in fishing gear and make swimming areas unappealing. Direct human health impacts are thought to be limited to eye irritation in swimmers.
Didymo feels like wet wool to touch, and is not slimy. Please report suspected masses of didymo. Help us confirm your report by collecting a small sample (put a pinch of the material in a business card and fold). Send samples with the date, latitude, and longitude (or detailed accurate site information).