Related Clues:

• White-water carriers
• Pond scum
• It may fill up your tank
• Seaweed, e.g.
• Pool owner's bane
• Floating platforms
• Pond greenery
• River floats
• Large quantities
• River transports
• Balsa vessels, e.g.
• Seaweed and kelp, e.g.
• Whitewater transportation
• Birdbath greenery?
• Sea moss, for one