The Mermaids are recurring characters from the Disney Channel series Phineas and Ferb, they come in light-tailed, lighter-tailed and dark-tailed and they heavily resemble Isabella and the Fireside Girls but as teenagers.
- Voyage to the Bottom of Buford (first appearance)
- Backyard Aquarium
- Phineas and Ferb the Movie: Across the 2nd Dimension
- One Good Turn (Lyla Lolliberry mermaid look-a-like)
- Isabella's Underwater Adventure
- Last Day of Summer (cameo) (appears in flashback(s))
- Phineas and Ferb the Movie: Candace Against the Universe