1- Place white icing and four to five drops of blue food coloring into a mixing bowl and use a rubber spatula to mix the icing and food coloring together. The icing will turn blue, meaning that it can used to simulate the look of water on the cake or cupcakes.
2- Place white icing and four to five drops of green food coloring into a mixing bowl. Mix the icing and food coloring with a rubber spatula. The icing will turn green and can be used to draw plants onto the cake or cupcakes.
3- Spread the blue icing over the surface of the cake or cupcakes with an icing knife, creating the look of a water backdrop.
4- Use a spoon to scoop the green icing into an icing bag, then use the icing bag to draw seaweed and aquatic plants along the base of the cake. On the cake, create as many seaweed or aquatic plant images as you think looks appropriate. On each of the cupcakes, draw only one aquatic plant to avoid cluttering the small space.
5- Place the Swedish Fish onto the surface of the cake and cupcakes. To ensure proper adherence, gently press the fish into the surface of the icing. Use the appropriate amount of Fish for the size of the treat. For example, on a cake, a small bag of candies can be used to mimic a school of fish swimming through the water. For cupcakes, place only one or two of the mini variety of Swedish fish on each to avoid overwhelming them.
6- Arrange the fish to suit your theme. For example, you can place individual fish onto the cake and draw the icing plants over them to create the look of fish swimming through plants. Alternatively, insert the candy into the cupcake's icing tail-first to create the look of the fish jumping out of the water. For large cakes, you can replicate the look of several schools of fish swimming around by placing small groupings of Swedish Fish on them.