- The Cast Show Off: Indiana Evans is a singer and sings the opening theme in the third season, as well as being shown singing at Rikki's club.
- Contractual Purity:
- Dawson Casting: Averted in the first two seasons as the three leading actresses were still in high school, but the gap between Seasons 2 and 3 left them playing high school seniors while they were 20/21 in the final season. Luke Mitchell is a straight example, being about 24/25 and playing a high school student.
- Doing It for the Art: Cariba Heine hired a professional trainer to help improve her swimming ahead of the audition.
- Dueling Dubs: Poland redubbed the first season when the show was put on Amazon Prime Video and Netflix.
- Fake Australian: Downplayed. Cariba Heine is South African born, though Rikki is a transfer student so she could be the same nationality as Cariba.
- Follow the Leader: This marked the third attempt at a mermaid drama in the 2000s. The CW had tried a pilot with Mermaid that wasn't picked up in 2001. Viacom tried in 2003 with Mermaids (which was also filmed in Australia) but ended up as a Made-for-TV Movie.
- I Am Not Spock: As she is the only one of the three leads not to act in America, Cariba Heine tends to be more associated with the show than the others. She appeared as Rikki in the spin-off.
- The Merch: CDs and books have become available in Australia; Kate Alexa's made herself famous by the CD. In the US, dolls of the 3 mermaids were available for a short time.
- No Export for You:
- In the US, the last half of Season 2 and the entire third season were held up substantially. The show ended half-way through Season 2 during re-airings in 2008. When TeenNick began re-airing the series in 2011, the remaining episodes still weren't being aired - instead cycling through the same aired episodes again and again. Finally averted on January 16, 2012, where the final thirteen episodes of Season 2 were aired in a TeenNick marathon leading into the US premiere of Season 3. (3 Years after the UK aired the 3rd season.)
- The rest of the world, including its native Australia, didn't get the 3rd season until 2010, whereas the UK got it first in 2009.
- Playing Against Type: Phoebe Tonkin would later get cast as lots of bitches or Action Girls. Her breakout role as Cleo is an Adorkable Shrinking Violet.
- Post-Script Season: Only two seasons were planned. But the sheer popularity of the show led to a third being commissioned, as well as two spin-offs. As a result, Claire Holt was already committed to a film in America when the third season was greenlit - resulting in Emma getting Put on a Bus and replaced with Bella.
- Real Life Writes the Plot: Lewis is Put on a Bus halfway through Season 3 because Angus McLaren was filming Packed To The Rafters.
- Reality Subtext: Phoebe Tonkin confesses to hating swimming before she was cast in the show, but grew to love it. Just like how Cleo grew to accept her mermaid powers.
- Retroactive Recognition:
- Emma's Season 2 Love Interest, Ash, became the True Seeker.
- American viewers watching on either The CW and/or Netflix may be surprised to see Claire Holt and Phoebe Tonkin, knowing them more for their recurring roles on The Vampire Diaries and their main roles in its spinoff, The Originals.
- As a child, Brittany Byrnes (Charlotte) played the Spoiled Brat granddaughter in Babe.
- Romance on the Set:
- Cariba Heine dated Jamie Timony, who played Nate, while the show was filming.
- Angus McLaren and Indiana Evans dated in real life too.
- Star-Making Role: For Claire Holt and Phoebe Tonkin.
- Vacation, Dear Boy: The actresses admitted to using the various beach scenes as excuses to have fun between takes.
- What Could Have Been: Gemma Forsyth was nearly cast as Charlotte before the role went to Brittany Byrnes. She would later get to play Evie in Mako Mermaids.
Trivia / H2O: Just Add Water