Where is Legionella bacteria commonly found?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Legionella bacteria commonly live in freshwater environments such as rivers and lakes, but they thrive most in man-made water systems, including cooling towers, hot tubs, decorative fountains, large plumbing systems, and hot water tanks. When these systems aren't properly maintained, Legionella can multiply and spread through tiny water droplets in the air, which people may unknowingly inhale.

If you've been exposed to any of these environments and are experiencing symptoms like cough, fever, or shortness of breath, it's important to act quickly. A free, instant, online symptom check can help you understand what may be causing your symptoms and guide you toward the right next steps—before things potentially worsen.

Reviewed for medical accuracy: 07/20/2026

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Explanation

Legionella bacteria are commonly found in various water environments. They thrive in natural water sources like rivers and lakes. However, they are also present in man-made water systems. This includes cooling towers, hot tubs, and plumbing systems, which provide conditions suitable for their growth.

Key Points:

Natural Water Sources: Rivers and lakes can harbor Legionella, as they naturally occur in these environments.
Man-Made Water Systems:
Cooling Towers: These are part of air conditioning systems and can spread the bacteria through water droplets in the air.
Hot Tubs: Warm water provides an ideal environment for Legionella to multiply.
Plumbing Systems: Stagnant water in pipes can allow the bacteria to grow, especially if the water temperature is between 77°F and 108°F.

Understanding where Legionella bacteria are found can help in taking preventive measures to control their spread and reduce the risk of infection. If you're experiencing symptoms that concern you, use our free symptom checker to help identify potential health issues.

(References)

Zhan XY, Yang JL, Sun H, Zhou X, Qian YC, Huang K, et al. (2022). Presence of Viable, Clinically Relevant Legionella Bacteria .... Microbiology spectrum, 35438512.
Stojek NM, & Dutkiewicz J. (2011). Co-existence of Legionella and other Gram-negative .... Annals of agricultural and environmental medicine : AAEM, 22216808.
Suzuki A, Ichinose M, Matsue T, Amano Y, Terayama T, Izumiyama S, & Endo T. (2002). Occurrence of Legionella bacteria in a variety .... Kansenshogaku zasshi. The Journal of the Japanese Association for Infectious Diseases, 12391673.

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