Related Clues:

• Organism that can be brown, red or green
• Pond problem
• Tank top?
• Snails' snack
• Fishtank growth
• Marine flora
• Aquatic organisms
• Lake floaters
• Bottom-of-the-food-chain organisms
• Pond organisms
• Birdbath gunk
• Aquarium buildup
• Big oxygen producer
• Bits of plankton
• Rootless sea life