It's not easy being the new mermaid in town, but Bella fits in quite easily. Confident, yet bubbly she is a singer and performs at the juice bar. She became a mermaid in the sea caves of Ireland when she was nine, and from the moment she shows up she has her eyes set on Will.
Special power: Bella can turn water into gelatin and a crystalline substance.
Typical Quote: "I'm guessing that's not normal?"
Bella possesses the ability to transform into a mermaid ten seconds after at the touch of water. Once her body is completely dry, she turns back into human along with the outfit she was wearing before she transformed. While in mermaid form, she can swim extremely fast at a speed of 600 km/h and hold her breath for almost 24 hours.
Bella's individual mermaid power is threefold, she can group together water particles to turn it into jelly, she can turn it solid hard with a fist gesture and waving her hand and she has the ability to explode water or jelly. Her power usually stops working after a few seconds, but if she concentrates on making it permanent, the water substance will remain in the same state forever. This is revealed when she and Cleo use their powers to make a birthday present out of water for Rikki; while Cleo shapes the present, Bella petrifies the water substance.
Bella develops a crush on free-diver Will almost as soon as she moves to town. Because he is often curious about what he "thinks he saw", Rikki always tells her to stay away from him to keep their secret safe. As they become closer, Will starts to have feelings for her. On one occasion, he accidentally drips water on her chin and she is forced to run into the ocean before she turns into a mermaid. Will then becomes suspicious of her and pours a glass of water on her hand, forcing her to transform in front of him. Although shocked at first, he agrees to keep her secret (though she keeps Cleo and Rikki's identities a secret).
However, Bella often hears Will talking about mermaids and the magic of it, she begins to feel that he is only interested in her because of her mermaid magic and breaks off their friendship. Eventually, they become friends again after Will finds out that Cleo and Rikki are mermaids as well. In one episode, she mistakenly hears Will asking Rikki to the party and decides to go with Nate to make him jealous. At the party, they clear the misunderstanding and become a couple officially.
Rikki Chadwick: [Bella is talking with Rikki, as Will and Sophie walk in and sit down] That's her.
Bella Hartley: You know, I'm going to say something.
Rikki Chadwick: Wait...
Bella Hartley: No, you were right about him.
Will Benjamin: Bella, I was just going to see you...
Bella Hartley: I know what you two were doing, Will, I saw you. And... I'm disappointed. I can't believe you lied to me to be with someone else. I thought maybe there could have been something between us.
Will Benjamin: [Tries to explain] Bella, ah...
Bella Hartley: [Interrupts] No! Don't try to squirm out of it. I thought you were different.
Will Benjamin: You did?
Isabel Hartley: Yes! But it just turns out that you're like all the other guys: selfish, lying, immature, two-timing...
Sophie Benjamin: ...and, he's my brother.
Bella Hartley: ...and, What?
Will Benjamin: Yeah.
Sophie Benjamin: That's right. I think you've made some kind of mistake.
Bella Hartley: Oh. Right. I guess, [laughs at her own foolishness] I guess I have. [Bella turns and walks to the far end of the juice bar, and puts her head down]