Paint the walls of the bathroom blue or green to create the backdrop for the seascape. Use dark colors for a deep sea look, although this can make a small bathroom look closed in, or light colors for an uplifting look. Aquamarine, deep blue and foam green all work for the sea-themed decor.
Stencil marine life onto the walls or paint them free hand if you have a steady hand. Use bright colors for a bathroom that is shared by the kids or choose more neutral colors for a mature bathroom. Add starfish, octopus, coral and a variety of fish to the wall. For an elaborate look, paint a coral reef starting at the bottom of the wall and build it up to the center.
Hang sea-themed items on the wall, such as seashell hooks or starfish wall hangings. Don't clutter the wall too much, just add enough to give it a three-dimensional look.
Complete the look by adding seascape shower curtain with marine life shower rings. Use towels the complement the decor such as sea foam towels with a blue bathroom.