Swimming Pool Granuloma: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 2, 2026.
What kind of doctor treats Swimming Pool Granuloma?
A primary care doctor, such as a family medicine or internal medicine doctor, usually treats this infection first. If it is deep, spreading, or not responding to treatment, they may refer you to a dermatologist or an infectious disease specialist.
What it is
Swimming pool granuloma is a skin infection caused by Mycobacterium marinum, bacteria related to the ones that cause tuberculosis. The germs live in fresh and salt water worldwide, and many people catch them while cleaning aquariums, which is why the condition is also called fish tank granuloma. The infection usually starts in a small cut, most often on the hands, arms, or elbows, and grows slowly over weeks or months.
Symptoms
The most common sign is a small, firm bump where the germs entered. It may look red, purple, or skin colored, and can turn into an open sore that usually does not hurt much. In some cases, more bumps appear in a line up the arm or leg, a pattern doctors call sporotrichoid spread; rarely, the infection spreads deeper in people with weak immune systems.
Causes and who gets it
The bacteria live in water and fish, and infection occurs when contaminated water touches broken skin. Common routes include cleaning fish tanks, handling fish, swimming in lakes or poorly maintained pools, or being scratched by a fish spine or shell. Aquarium owners, fishermen, fish market workers, and people with weakened immune systems face the highest risk.
How doctors diagnose it
There is no single quick test, so doctors start by asking whether the sore appeared after contact with water, fish, or an aquarium. To confirm the cause, a doctor may take a sample of tissue or fluid for a culture, which can take several weeks because the bacteria grow slowly. A skin biopsy may help rule out other conditions.
Treatment
Treatment usually involves antibiotics, often more than one at a time because the germ can resist single drugs, and commonly lasts several weeks to a few months. Sores that do not respond to medicine may need minor surgery to remove infected tissue.
When to see a doctor
See a doctor if a sore or bump does not heal after a couple of weeks, especially after contact with fish tanks, lakes, or pools. Also seek care if a sore grows or spreads, or if you have a weakened immune system, since early treatment makes the infection easier to clear.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor charges more and often works alongside insurance. Either can often manage this infection from start to finish, ordering labs, prescribing antibiotics, and monitoring healing over weeks of follow-up, and will refer you to a specialist if needed.
Common questions
Is swimming pool granuloma contagious from person to person?
No, it almost never spreads between people. The infection comes from water or fish carrying the bacteria, so normal contact with an infected person is not a concern.
Can it go away without treatment?
It usually does not clear on its own and can last for months or years if untreated. Doctors generally recommend antibiotics, since waiting can let the infection spread deeper.
How can I prevent it?
Wear waterproof gloves when cleaning a fish tank or handling fish. Wash cuts right away if they touch aquarium, lake, or pool water, and keep open wounds covered before swimming.
Sources
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
