A green pool represents a serious water quality failure that makes swimming unsafe. The distinct color signals a chemical imbalance that compromises the water’s ability to sanitize itself. This environment is conducive to the rapid growth of harmful pathogens and microorganisms that pose a direct risk to human health. Until the water is crystal clear and chemically balanced, avoid entering the pool entirely.
What Causes a Pool to Turn Green
The most common reason pool water develops a green tint is the proliferation of algae, a microscopic organism. This bloom is triggered by a lack of free chlorine, the active sanitizer, which allows algae spores to multiply unchecked. Chlorine becomes less effective when its level drops below 1 part per million (ppm) or when the water’s pH level rises above 7.8. Warm water combined with insufficient sanitizer creates an ideal breeding ground.
Other factors can contribute to discoloration, even without a major algae bloom. High levels of metals, particularly copper, can react with chlorine or other oxidizers, giving the water a greenish-blue hue. Environmental debris such as fine pollen or tannins from nearby plant life can also lend a light green or yellowish cast. In all cases, the green color is a diagnostic sign of chemical instability and poor filtration.
Specific Health Hazards of Green Water
Swimming in green water exposes individuals to an elevated risk of recreational water illnesses (RWIs). When sanitizer levels are low, bacteria like E. coli and parasites such as Giardia and Cryptosporidium thrive. Ingesting contaminated water can lead to severe gastrointestinal distress, including diarrhea, vomiting, and abdominal cramps. Cryptosporidium is particularly concerning because its oocysts are highly resistant to standard chlorine levels and can survive for days.
Beyond the internal risks, the water’s chemical imbalance and high microbe count cause immediate physical irritation. Swimmers may develop skin rashes, hives, or dermatitis from contact with the high bacteria load and unstable pH. The eyes and ears are also susceptible to infection, leading to painful conditions like swimmer’s ear or conjunctivitis.
A green pool also presents a severe physical safety hazard due to reduced visibility. Murky water obscures the bottom of the pool, making it impossible to see a person who may be struggling underwater. This lack of clarity significantly increases the risk of drowning, especially for young children or pets, as precious seconds are lost trying to locate them.
Immediate Care Following Accidental Exposure
If you or someone in your care has swum in green pool water, immediate and thorough rinsing is necessary. Exit the pool and shower with soap and warm water to remove lingering bacteria, algae, or residual chemical irritants from the skin. Flush the eyes with clean water for several minutes if irritation or redness is present.
Following exposure, monitor for symptoms of recreational water illness for up to two weeks. Watch for signs of gastrointestinal distress, such as persistent diarrhea or vomiting, fever, or a severe skin rash. If these symptoms develop, contact a healthcare provider immediately and mention the exposure to contaminated pool water.
How to Safely Restore Pool Clarity
Restoring a green pool requires a systematic approach, starting with a comprehensive water test. First, check and adjust the chemical balance, ensuring the pH is maintained between 7.2 and 7.6 and the alkalinity is between 80 and 120 ppm. Effective chlorination is severely limited if these levels are outside the proper range.
Once the balance is achieved, the pool must be super-chlorinated, known as shocking, which involves adding a large dose of chlorine to kill algae and pathogens. This super-dose is most effective when applied at dusk or night, as sunlight rapidly degrades chlorine. Also, physically scrub the pool walls, steps, and floor with a brush to dislodge clinging algae and allow the sanitizer to reach it.
After shocking, run the pool’s filtration system continuously, ideally for 24 hours or more, to circulate the treated water and filter out dead algae particles. Backwash the filter as necessary to maintain proper water flow and pressure. The pool is not safe for swimming until the water is completely clear, the chlorine level is back in the normal range (1 to 3 ppm), and the chemical balance is confirmed with a second test.