Related Clues:

• Snails' snack
• Fishtank growth
• Marine flora
• Bathtub residue
• Aquatic organisms
• Dirty film
• Lake floaters
• Bottom-of-the-food-chain organisms
• Pond organisms
• Birdbath gunk
• Aquarium buildup
• Big oxygen producer
• Lowlifes
• Bits of plankton
• Slimy film