How do I make a a water background look more freshwater theme and not ocean theme?

So I’m planning on painting a background for a custom doll box, and I could use some advice.

So I’m thinking some cartoon piranhas in the background since piranhas are freshwater fish, but that could easily be mistaken for barracudas, and my biggest thing is what color the water should be.

I’m thinking about adding in some green for algae, I was thinking seagrass at the bottom, but I’m gonna be using acrylic paint for this and I just don’t really see a vision for how I would do that.