· Warm up with 50 jumping jacks in dry sand.
· Sprint barefoot from shoreline into sea until you're waist-deep. Sprint back. Repeat 10 times.
· Return to dry sand for 20 walking lunges.
· Head back into water with a beach ball. Hold ball between the knees and swim with arms only: 30 strokes freestyle, 30 strokes backstroke, 30 strokes breaststroke.
· Repeat steps 1 through 3 until half-hour is up.