Swimming is the gentlest of all aerobic activities. Unlike running, it doesn't have a negative effect on your bones and joints over time, and yet it makes a positive impact on your fitness and health. Water is healing, and swimming is especially recommended for those who want to prevent injury, use it for cross-training, are pregnant, are recovering from an injury, are suffering from joint or bone conditions, or are overweight and want to exercise in a weightless environment. You can build muscular strength and endurance, as well as improve flexibility and cardiovascular fitness, through swimming.