I do a great deal of aquatic programming. I recommend that you experiment with different movements in the water and get a feel for ways to be innovative while still working the target muscles for any exercise. There are so many ways to put the unique qualities of aquatic exercise to work for you. Get in and play around.
I will give you a great core exercise to use in the water. While water jogging (deep or shallow water), sweep the water from side to side with the hands. The arms can be bent keeping the sweep close to the body. Or the arms can be fairly straight (don’t lock out the elbows), sweeping a big arc. Intentionally engage the core to minimize rotation of the spine for stability training. And use an engaged core while slowly twisting at the waist for dynamic core work. Cue for no breath holding and feeling the torso muscles engaging. This can be done in a stationary position as well.
I teach CECs on aquatic exercise in Hawaii. If you ever make to the Big Island check out my website, www.hawaiifitnessacademy.com , and get in touch with me. You can take a course or just come watch one of my classes.