Updated: May 14, 2020
Fresh water sponge spotted on Rocky Reef by Maria Gross
Freshwater sponges are usually pencil-shaped green structures attached to underwater brush or logs. They can also be shapeless green “spongy” masses covering rocks like the sponge shown here. Sponges are filter feeders. They obtain food from the flow of water through their bodies and from symbiotic algae. Their green coloration usually comes from the encapsulated algae cells. For this reason, many people mistake freshwater sponges for algae, but sponges have a coarse texture, and are not slimy like algae.
Because they are sensitive to water conditions, their presence indicates clean, clear water.