There is lots you can do:
the same action of skipping including your arms so you dip under water then up in the air
kick your leg & reach out with your opposite arm then swap to the other side
if you have pool noodles push the noodle up & down under the water
use the pool noodle to push out in front of you just below the water surface
in the deep end with your arms out streched on either side of you then tuck your legs up to your chest & push your legs out to one side tuck back under then stretch out to the other side (without touching the ground at all). It's hard but very good for your core
depending on how big your pool is but run around the edges of your pool to create a whirl pool then change directions. Good for your legs.
That's all I can think of that I do but pretty much anything that your constantly moving & creating friction with the water is good exercise.