Yes, I've seen Splash!, and I've adored Disney's The Little Mermaid for years. But Splash! wasn't about the underwater world, just about the mermaid's adaptation to land. Even at the end, when Tom Hanks follows her back into the sea, we don't really see the world they go to. And The Little Mermaid was far more concerned with the merpeople's distrust of humans because they eat fish, or a girl's desire to break the rules--oh, and the way Ariel's hair twirled around in the water (visually spectacular, but not something that will transfer well to a novel format). None of this will really speak to what I hope to write.
Uncharted territory. I like it. Even better, it's uncharted territory with rules, like writing a sonnet, for I have to obey the rules of undersea life at least to an extent so that nothing sticks out as stupid.
It also means I can't just throw myself into writing. I need to figure out setting, create the lifestyle, and decide what rules I need, what rules I can break, and how everything is going to fit together. I need to do quite a bit of world building.
I'm getting giddy just thinking about it!