Didymo

Didymo, also known as didymosphenia geminata, is a single-celled alga that forms large, dense mats in freshwater rivers and streams. It is commonly referred to as "rock snot" due to its appearance, which can resemble clumps of brown or green mucus clinging to submerged surfaces. These mats can cover streambeds, rocks, and aquatic vegetation, impacting the habitat for native species.

The organism is native to the Northern Hemisphere but has spread to various parts of the world, including New Zealand, Australia, and parts of North and South America. Its spread is primarily attributed to human activities, such as the movement of contaminated fishing gear, waders, and boats.

Didymo thrives in clear, cold, nutrient-poor waters, often in oligotrophic or mesotrophic streams. While it is a natural component of aquatic ecosystems, its rapid proliferation into dense blooms is considered an invasive issue. These blooms can alter stream habitats by smothering invertebrates and reducing food availability for fish. They can also interfere with recreational activities like fishing and swimming by making surfaces slippery.

Preventing the spread of didymo is crucial. Authorities often advise anglers and boaters to thoroughly clean and dry all equipment before moving between waterways. This involves scrubbing, rinsing with hot water, and allowing gear to dry completely for an extended period. Monitoring and early detection are also key to managing its impact.