This was a birthday party for a tween girl who adores the ocean and the color blue. I created a "blue room" by hanging up blue curtains in the window and a curtain of tri-colored streamers in the arch separating the party room from the next room in the house. The circle streamers and balloons were there as "bubbles", and the fishing net and sea shells scattered throughout further enhanced the oceanic atmosphere.
The decor as well as the cake were kept simple and "grown up", and I stayed as far as possible from the cartoony ocean theme usually seen for little boys. I wanted this to be a girly ocean theme, and the birthday girl loved it!