When fecal matter enters a swimming pool, it poses an immediate public health risk, which pool managers call a Fecal Incident (FI). Although the pool’s chemistry, primarily chlorine, is designed to disinfect the water, this process is not instantaneous, creating a window for illness transmission. Swimmers primarily contract a Recreational Water Illness (RWI) through the accidental ingestion of contaminated water, even in small amounts. The resulting danger depends heavily on the type of infectious agent present and its ability to withstand standard chlorine levels.
The Primary Health Risks
The most significant danger from a fecal incident comes from microorganisms that can survive in chlorinated water for extended periods. The parasite Cryptosporidium parvum, or “Crypto,” is the most common cause of diarrheal outbreaks linked to swimming pools because it is highly resistant to chlorine. A single diarrheal incident can release millions of infectious oocysts that can survive in properly chlorinated water for more than ten days. Other concerning pathogens include the bacterium Escherichia coli (specifically E. coli O157:H7) and the parasite Giardia intestinalis. While most E. coli strains are killed quickly, Giardia is more robust, typically requiring around 45 minutes to be inactivated by standard chlorine concentrations.
Common Symptoms and Illnesses
Exposure to these fecal pathogens leads to Recreational Water Illnesses (RWIs), which are primarily gastrointestinal. The most common symptoms include watery diarrhea, stomach cramping, nausea, vomiting, fever, and dehydration. The incubation period varies by pathogen: cryptosporidiosis symptoms typically appear about one week after exposure, while giardiasis usually takes one to two weeks to manifest.
While most cases are self-limiting, the illness can last for two weeks or more. Swimmers should seek medical attention if symptoms are severe, such as bloody diarrhea, persistent high fever, or signs of severe dehydration. People with compromised immune systems, young children, and pregnant women are at a higher risk for more serious, prolonged illness.
Immediate Pool Response and Remediation
When a fecal incident occurs, the pool must be immediately closed to all swimmers. The operator’s response depends heavily on whether the fecal matter is solid (formed stool) or liquid (diarrhea). Formed stool is lower risk because germs are contained within the solid mass, while diarrheal matter rapidly releases pathogens into the water. For any incident, the fecal matter must be removed using a net or bucket and disposed of sanitarily.
Formed stool incidents require disinfection to inactivate Giardia by raising the free chlorine concentration to 2 parts per million (ppm) and maintaining a pH of 7.5 or less for 25 to 30 minutes. Diarrheal incidents require hyperchlorination, a more aggressive chemical treatment necessary to inactivate Crypto. This involves raising the free chlorine concentration significantly, often to 20 ppm or higher, while maintaining the water temperature at a minimum of 77°F (25°C) and a pH of 7.5 or below. For sufficient Crypto inactivation, 20 ppm free chlorine must be maintained for at least 12.75 hours, or 40 ppm for approximately 6.5 hours.
Preventing Future Contamination
The most effective way to protect swimmers is to prevent fecal matter from entering the water. Swimmers should practice “Healthy Swimming” habits, starting with a thorough shower using soap before entering the pool. This action removes fecal material, sweat, or dirt that can otherwise use up the pool’s chlorine.
Anyone who is ill with diarrhea should not swim; for confirmed cryptosporidiosis, a person should wait up to two weeks after symptoms have completely stopped before returning to the water. Swallowing pool water should be avoided, as this is the primary route of infection. Pool operators should encourage frequent bathroom breaks for young children and ensure that children’s diapers are changed away from the poolside area.