I got the idea for this lesson when I was reading the picture book "Swimmy" by Leo Lionni to my Kindergarten class a few years ago. Leaf through "Swimmy" while pointing out the various forms of plant life depicted in the illustrations to students. Ask students how they think the illustrator created those images. Challenge the children to create various types of seaweed by painting a variety of lines (eg, different colors, wavy lines, zigzag lines, curly lines, crisscrossing lines) that extend from the top of the paper to the bottom.
They will first paint the water background with their watercolors and then when that is dry they can add the seaweed and fish using the drybrush method. This method is created when students use their fingers to squeeze the extra water from the brush prior to painting.
An extension of this lesson might be to create not only the seaweed, but other plant forms found in the book. Students would use Tracing Paper and Tissue paper when they create their objects. The tissue paper is then glued on a frame and a light source is held behind it to light it up (See above). The fish might be animated by using sticks that can be used in a theater production the kids create. Use the PDF documents below for resources for your theater production. (Photo from Kids Entertainment. They have other resources for purchase there.)
Swimmy Resources Guide - This PDF resource by Mary Langille includes the integration of theater, mathematics, music, and science.