When people think of water-based exercise, swimming usually comes to mind. But that’s just a drop in the bucket. There’s also walking or running under water and water aerobics classes.

According to the Aquatic Exercise Association, you can expect to burn 400 to 500 calories per hour when exercising in the water. Also, water offers 12 times the resistance of air, which helps strengthen muscles. Boost the resistance and intensity of pool exercises by adding handheld paddles, kickboards, foam noodles and rings to your aquatic workout. And when you’re done, stay in the pool. It’s a great place to do stretches to improve flexibility.

It’s easy to jump into a water-based exercise program—you don’t need fancy equipment or previous training. Check with your local health club or recreation center for details. And remember, many centers require a physician’s approval before they permit you to dive into the pool.