Water aerobics combines cardiovascular exercise with strength training for a low-impact, full-body workout. By exercising in water, you take advantage of the water's resistance to strengthen your muscles as you move.
This form of exercise has become the stereotypical senior workout, but with good reason. Like with swimming, the water takes stress off of your joints and allows you to build strength and endurance with very little impact. It's a common misconception that you need to be able to swim to participate in water aerobics classes. Most take place in shallow water -- between waist and chest deep -- so swimming is not a requirement.
You can find water aerobics classes at gyms, the YMCA and community pools. Some cities offer low- and even no-cost water aerobics classes for seniors, making it easy to get started. Check with local community centers or your city's parks and recreation department to see what's offered in your area.