Possible Clues:

• Simple organisms, e.g. seaweeds
• Seaweed, e.g.
• Stagnant-water buildup
• Photosynthetic organisms
• They grow near water and don't have ordinary roots or leaves
• Seaweeds, et al.
• Swimming pool concern
• Rootless life of the sea
• Seaweed and kelp, e.g.
• Aquarium issue