Floating mat of filamentous green algae in Dolloff Cove - photo by Don Yurewicz
Filamentous algae consists of single algae cells that form long visible filaments that intertwine forming soft green mats. It starts growing along the bottom in shallow water or attached to structures in the water (like rocks or other aquatic plants). On warm, sunny days, they commonly float to the surface when bubbles, generated by the plant or created by its decay, get trapped in the mats and make them buoyant (see photo above). There are many species of filamentous algae and often more than one species will be present at the same time in the pond.
Filamentous green algae are naturally occurring and are not harmful. It is not a Cyanobacteria which can have toxins associated with them, including neuro- and hepatotoxins, that can be harmful to humans and animals when present in high concentrations. It can, however, become a nuisance to swimmers, fishing and lake aesthetics if it becomes too abundant. Overproduction of algae is often tied to excessive nutrients (phosphorous and nitrogen) introduced to the lake by runoff from fertilized lawns and fields.
Webinar - Filamentous Algae (Metaphyton) in Main Lakes: A Presentation from Lake Stewards of Maine
For more than a decade, public anecdotal observation has suggested that metaphyton, aka green filamentous algae, has been increasing in Maine lakes. But is it – and if it is, should we be concerned? Citizen scientists can play an important role in answering these persistent questions.