Massage your thighs in a do-it-yourself whirlpool
Walk as fast as you can in a circle around a section of the pool that's about 3 feet deep (the more people, the better the effect). Do about 20 laps, then change direction for 10 laps. The resulting rush of water against your body will feel much like the jets in a whirlpool.
A Game of Fetch
Torch 175 calories in just 20 minutes
Throw an inflatable ball to the other side of the pool and see who can retrieve it the fastest. You won't even notice you're doing sprints.
Visiting a Water Park
Boost your butt with a fun stair workout
You may climb more than 800 steps to reach the water slides and walk 5 to 7 miles during a 1-day visit. And the ride down will cool you off.
Target your fat-burning leg and butt muscles
You'll easily glide through the water with a kickboard or noodle in hand. Practice different types of kicking: flutter (alternating legs), dolphin (legs together, mermaid style), and breaststroke (frog kicks), suggests Paul Smith, swimming instructor and fitness specialist at Lake Austin Spa Resort in Austin, Texas.
Burn a whopping 750 calories an hour
Hold a noodle or slip on a flotation belt or vest. "Run" as hard as you can for 30 to 60 seconds, bringing knees toward chest and pumping your arms. Do 10 sets, recovering your breath between sprints, suggests exercise physiologist and triathlon coach Ben Greenfield of Spokane, Washington.
A Beach Ball Workout
Tone your arms and shoulders—no throwing (or catching) required
Trying to submerge a ball that floats really works your core and upper body. Experiment with different movements to vary the muscles targeted, says Sanders. For example, press a small ball down in front of you with bent arms, then move it to the side and straighten arms.
Work more muscles for speedier results
Research shows that water walking or jogging in reverse engages more muscles in your legs and back than going forward (83 percent more quads, 61 percent more lower back, and 47 percent more calves).
Slim down saddlebags
To tone your inner and outer thighs, shuffle side to side in at least thigh-deep water, says Melissa Layne, an American Council on Exercise spokesperson and a water aerobics instructor for 20 years. Keep movements smooth.
Firm up as you chat—no one will notice!
Stand in chest-deep water with palms open and fingers spread and move your arms back and forth and up and down. Increase your speed for a greater challenge. More from Prevention: For more tips on how to shape up all summer long, try our reader-tested beach-body workout.
More: Get Gun-Show Biceps
Stay in shape in a fitness class.