Algae are simple, plant-like organisms that can quickly transform a clear swimming pool into a murky, discolored body of water. While the algae itself is generally not toxic, the presence of an algae bloom indicates a failure in the pool’s sanitation system. For this reason, it is not safe to swim in a pool with algae. The problem is not the green substance but what that substance signifies: a breakdown in the water chemistry that normally keeps the water safe for human contact.
The Real Health Risks of Swimming in Algae Water
The growth of algae provides a clear signal that the pool’s primary defense against harmful microorganisms has been compromised. Algae spores thrive when the sanitizer levels, typically chlorine, are too low or non-existent, or when the pH balance is incorrect. This lack of proper disinfection creates an environment where dangerous waterborne pathogens can multiply rapidly.
When chlorine is depleted, the pool becomes a breeding ground for bacteria, viruses, and parasites that cause recreational water illnesses (RWIs). Pathogens such as E. coli, Giardia, and the highly chlorine-tolerant parasite Cryptosporidium can survive and flourish in these conditions. Swallowing even a small amount of this contaminated water can lead to infection.
Symptoms of RWIs primarily involve the gastrointestinal system, including diarrhea, nausea, vomiting, and abdominal cramps. Contact with the contaminated water can also cause painful skin infections, such as folliculitis, or irritations like Swimmer’s Ear and conjunctivitis (pink eye).
Non-Health Hazards and Pool Damage
Beyond the invisible threat of waterborne pathogens, an algae bloom introduces distinct physical safety risks. Algae, particularly the fast-growing green variety, form a slick, slimy biofilm on pool surfaces like the floor, steps, and ladder rungs. This biofilm dramatically reduces traction, creating a serious slipping hazard that can lead to falls, bone fractures, or head trauma.
The second major physical risk is the loss of visibility within the water column. Even a moderate algae bloom causes the water to become cloudy, obscuring the view to the bottom of the pool. This lack of clarity is a serious drowning hazard because it makes it impossible to spot a swimmer in distress or unconscious beneath the surface.
Algae also has a destructive impact on the pool’s mechanical circulation system. The debris and spores from the bloom are pulled into the filtration system, quickly clogging the fine media in sand, cartridge, or diatomaceous earth (D.E.) filters. A clogged filter restricts water flow, forcing the pump to work harder to circulate the water. This strain increases energy costs and accelerates wear and tear on the pump motor, potentially leading to premature equipment failure.
Practical Steps to Eliminate Algae
The process of eliminating algae must begin with a thorough testing and balancing of the water chemistry. Sanitizer effectiveness is heavily dependent on the water’s pH and alkalinity levels, so these must be corrected first. Ideally, the pH should be adjusted to a range between 7.4 and 7.6, while the total alkalinity should be maintained between 80 and 120 parts per million (ppm).
After balancing the water, the pool must be aggressively “shocked” with a high dose of chlorine to kill the living algae cells. This super-chlorination process is most effective when performed after sunset, as the sun’s ultraviolet rays rapidly degrade the chlorine before it can fully sanitize the water.
The next immediate step is to vigorously brush all pool surfaces, including the walls, floor, and steps, to dislodge the dead algae and break apart any protective layers. This is especially important for stubborn black or mustard algae varieties.
Following the chemical treatment and brushing, the pool’s filter should be run continuously for at least 24 to 48 hours to remove the dead particles. To accelerate the cleanup of cloudiness caused by dead algae, a clarifying agent can be introduced. A clarifier works by binding microscopic particles together, making them large enough for the filter to capture.
For pools with very dense blooms, a flocculant may be used to quickly sink the debris to the bottom, requiring a manual vacuum to waste the material. After the water has cleared, maintaining a stable chlorine level, typically 1 to 3 ppm, along with daily pump operation and routine brushing, is necessary to prevent any recurrence.