When the steamboat comes out, all the characters are on it. As the boat makes its way around to the other side, we all know that the next scene is the big fireworks finale. Well, when the boat reaches near the very end of its voyage, the fireworks start going off. All the characters on the boat go inside the boat because that area is a fireworks fall out zone.
Unfortunately, of all the characters on the boat, only one doesn't have legs to walk: Ariel from The Little Mermaid. She sits on the back of the boat on the 2nd level. If you watch closely, they have to put a fire-proof blanket over her so she can sit there still protected as the fireworks shoot off.