Actually, anyone who comes in contact with the magic water on Mako Island will become a mer-person, but it never happened to a guy on the original series.
Here the protagonist is Zac (Chai Romruen), who becomes a merman after falling into the magic Moon Pool. He heads back to Australia, trailed by three mermaids, Sirena, Nixie, and Lyla, who want to take away his merman powers. They eventually befriend him and start dating mortal boys.
The mythology is further developed, with mermaid society skirmishes, dark secrets from the past, and a mysterious trident that may be the key to everything.
Heteronormativity still reigns supreme, but there's a tiny bit of homoerotic buddy bonding between Zac and his mate Cam (Dominic Deutscher), who quickly discovers his secret.
And Eric (Alex Cubis), a mysterious figure who belongs to a rival mermaid pod.
Plus, the beefcake quota is even higher. In addition to Zac, Cam, and Eric:
Gabe (Chris Cocciolone), a lifeguard.
Karl (Mikey Wulff), a marine park worker.