Legionella is a type of bacteria commonly found in freshwater environments, such as lakes and rivers. It can also thrive in man-made water systems, including hot tubs, cooling towers, and plumbing systems. When people inhale aerosolized water droplets containing the bacteria, they can develop a serious form of pneumonia known as Legionnaires' disease. This disease can cause symptoms like cough, fever, and difficulty breathing. While anyone can get infected, those with weakened immune systems, older adults, and smokers are at higher risk. Preventing Legionella growth involves maintaining proper water temperatures and regular cleaning of water systems.