Freshwater Sponge

Spongilla lacustris

The freshwater sponge (Spongilla lacustris) is one of the most widespread freshwater sponge species, found in lakes, rivers, and canals throughout the Northern Hemisphere. It forms encrusting or branching growths on submerged rocks, wood, and other hard surfaces, typically reaching 10-30 cm across though larger colonies exist. Its color ranges from white to grey, but most commonly appears bright green due to symbiotic algae (zoochlorellae) living within its tissues, which photosynthesize and provide the sponge with additional nutrients. The texture is soft and slightly fuzzy, supported internally by microscopic siliceous spicules. Like all sponges, it is a filter feeder, drawing water through countless pores and extracting bacteria, algae, and organic particles. Freshwater sponges reproduce both sexually through tiny larvae and asexually through gemmules, tough resistant buds that survive winter freezing and drought before germinating in favorable conditions. Freshwater divers may encounter these sponges on submerged logs, bridge pilings, and rocky surfaces in clean lakes and rivers, where they indicate good water quality.