Related Clues:

• Chlorophyll-containing microorganism
• Lake floaters
• Bottom-of-the-food-chain organisms
• Pond organisms
• Spirogyra, e.g.
• Birdbath gunk
• Aquarium buildup
• Big oxygen producer
• Lake organism
• Bit of ocean life
• Bits of plankton
• Primitive plant
• Simple aquatic organism
• Rootless sea life
• Birdbath organism