How does didymo affect the physical condition of a riverbed?

Didymo, also known as "rock snot," is a type of freshwater algae that can significantly alter the physical condition of a riverbed. When didymo blooms in large quantities, it forms dense mats that cover rocks and substrates. This growth creates a slippery surface, making it difficult for fish and other aquatic organisms to navigate. The slippery mats can interfere with the natural movement patterns of fish, disrupt spawning behaviors, and impact the overall biodiversity of the river ecosystem.

While some might consider that it could prevent erosion or improve habitat for fish, these outcomes are generally not observed in environments heavily impacted by didymo. Instead, the slick mats can hinder the health and diversity of habitats because they restrict access to substrates that many organisms rely on. Similarly, the role of didymo in filtering pollutants is not effectively recognized; instead, it often contributes to negative ecological impacts when present in excess.