Swim Workouts That Work your Lower Abs and Buttocks

What workouts work out the lower abs and buttocks? I'm particularly interested because I have been training so hard using SDK and other drills to get rid of the minor gut that I do have, but to no real success. What about your butt? I want a tight small butt. Is running and using the butt blaster machine the only way? My diet is fine, if you're wondering. Thanks! Love to read your thoughts!