Swimming in a green pool should be avoided. The vibrant, often murky green color signals that the water chemistry is severely compromised and sanitation has failed. This coloration indicates a high concentration of contaminants, ranging from biological organisms to oxidized metals. A green pool is a serious indicator that the water environment is now an active breeding ground for pathogens.
What Makes Pool Water Turn Green
The most prevalent cause of green pool water is algae growth, which occurs when the disinfectant level, typically chlorine, drops too low. Algae are microscopic photosynthetic organisms that thrive in warm water and sunlight, quickly multiplying to turn the water cloudy green, yellow, or sometimes black. While this organic material is not inherently toxic, its presence confirms the pool’s water balance has been lost, creating an environment where harmful microbes can flourish.
Sometimes, the water may appear green but remain relatively clear, pointing to a chemical issue rather than an algae bloom. This coloration is often caused by the oxidation of metals, primarily copper or iron, introduced from the source water or corroding pool equipment. When the pool is shocked, these metals precipitate, giving the water a light green or turquoise tint. Pollen can also contribute a yellowish-green hue, as its particles are often too small for standard filters to capture. A green pool signals that the water is unsanitized and requires immediate professional attention.
Immediate Health Risks of Swimming in Algae
The most significant danger of swimming in unsanitized green water is contracting a Recreational Water Illness (RWI). These illnesses are caused by germs spread by swallowing or having contact with contaminated water. The lack of proper disinfectant allows bacteria, viruses, and parasites to survive and multiply.
Bacterial Infections
A common threat is the presence of Pseudomonas aeruginosa, a bacterium that causes skin infections, notably folliculitis, often called “Hot Tub Rash.” This bacteria is also responsible for Swimmer’s Ear, an infection of the outer ear canal. Unsanitized conditions also enable the spread of gastrointestinal pathogens, such as E. coli and Salmonella, which cause diarrhea, vomiting, and stomach cramps if contaminated water is swallowed.
Parasites and Chloramines
Parasites like Cryptosporidium (Crypto) and Giardia are concerning because their protective shells make them highly resistant to standard chlorine levels. These parasites can persist for days, causing widespread diarrheal illness.
The volume of organic matter, such as algae and decaying debris, consumes available chlorine, producing irritating chemical byproducts known as chloramines. These compounds are responsible for the strong, pungent “chlorine smell” and can cause eye irritation, skin dryness, and respiratory discomfort.
The Danger of Reduced Visibility
Beyond the biological and chemical threats, the opacity of green water introduces a risk of drowning. The cloudiness, known as turbidity, prevents clear sightlines to the bottom of the pool. A struggling swimmer or a person submerged beneath the surface can easily be obscured by the green haze.
This lack of visibility makes it nearly impossible for parents or lifeguards to spot a swimmer in distress quickly enough to initiate a timely rescue. Drowning is swift and often silent, and every second counts in a rescue scenario. The inability to see a submerged body means that a life-threatening emergency may go entirely unnoticed until it is too late. Health codes often require that the deepest point of the pool must be clearly visible from the deck, a standard a green pool cannot meet.