Related Clues:

• Film bit
• Green organism
• It grows on rocks
• Damp area growth
• Unwanted organism in an aquarium
• "A rolling stone gathers no ___"
• Lake plant
• Fungus-alga union
• Velvety green growth
• Pool organism
• Reindeer moss, e.g.
• Part of many a snail's diet
• Shady growth
• Stagnant water problem
• Gala class of seaweed