Using an oblong seedless watermelon, cut a 1/4-inch slice off the bottom to provide a stable base. Draw lines in a wave design with a sharp pencil or thin marker approximately one half of the way up and all the way around the watermelon.
Scoop out the flesh with an ice cream scoop or a large spoon, and reserve for salad.
Chill gelatin in a small plastic container to make a pool of “water” and place in the watermelon bowl. Fill in around the “water” with fruit salad cut into fun shapes and balls.
Arrange toys toward the edge of the watermelon bowl. Garnish sides with drink umbrellas and plastic palm tree swizzle sticks, and add gummy fish to complete the scene.