| Clue | Source | Date |
|---|---|---|
| Blue-green scum on water, from pollution/rising temperatures (5, 5) | ||
| A coloured scum on the surface of water from aquatic organisms (5,5) | ||
| Harmful aquatic overgrowth | New York Times | 11 Jun 2023 |
| Potentially destructive marine growth | New York Times | 04 Feb 2022 |
| Rapid green growth in a lake or pond | ||
| Rapid green growth in a lake or pond | New York Times | 11 Nov 2019 |