Related Clues:

• Pond growths
• Pond coating
• Life on the water
• Sushi ingredient
• Pond scum
• It may fill up your tank
• Seaweed, e.g.
• Pond greenery
• Seaweed and kelp, e.g.
• Birdbath greenery?
• Sea moss, for one
• Pool-owner's problem
• Pool growths
• Phycologist's study
• Aquatic plants