Not All Algae Is Harmless — Here’s When It Becomes a Real Health Threat

During a time when the Reflecting Pool at the Lincoln Memorial in Washington has thrust the topic of algae into the national conversation, pool owners can only nod in recognition, because they’ve been dealing with it all along. Dreading the appearance of even a hint of green, they know a budding algae problem can quickly get worse, and if they don’t do something about it, the water can actually become a health hazard.

A swimming pool has a small fraction of the water of the Reflecting Pool, but controlling algae can still be a chore. To get a handle on the algae problem — what it is, why it happens and what to do about it — we checked in with Graham Banks and Rafi Friedman, two pool contractors from Florida, Brock Falk, a pool care manager from Arizona, and Randy Huckstadt, a consultant with 20 years experience in the pool industry.

What Is Algae, and Why Does It Thrive in Pools?

Algae is a microscopic plant, and like all plants, it blooms when it gets three things: food, warmth, and sunlight. “In a pool,” explains Banks, “the food is usually phosphates, and the two biggest sources are rain and lawn fertilizer. Storms wash phosphates out of the air and off the deck, and fertilizer applied to nearby lawns and landscaping drifts and runs straight into the water. That’s why a pool so often turns green a day or two after a heavy summer downpour or a fresh lawn treatment, even when the chlorine looked fine the day before.”

Pool water usually contains a sanitizer like chlorine, and as long as the pool owner maintains the proper levels, it controls most algae growth. However, chlorine breaks down in direct sunlight, and algae blooms become more common in summer unless the a chlorine stabilizer like cyanuric acid (CYA) is added to the pool water.

Nuisance Algae vs. Toxic Algae: What’s the Difference?

Most algae is nuisance algae, according to Huckstadt, and that includes green, yellow (mustard), and black algae. “It’s costly to clean up, clouds water, makes surfaces slippery, and consumes sanitizer, but it is not inherently toxic to humans.”

Blue-green algae is a different thing altogether. It isn’t actually an algae at all, but a bacteria that produces hazardous cyanotoxins.

How to Tell When Algae Is Toxic?

“You can’t tell when algae is toxic,” warns Falk. “Visible algae is the first sign your pool can harbor bacteria, which is the dangerous part. If you see algae, it’s better to stay out of the water until it’s treated.” Even though all algae is potentially dangerous, you can be sure you have a problem if you see these signs.

Blue-green color

Blue-green algae is “easy to spot because of its telltale color,” says Friedman, “but you can also buy water test kits to eliminate any doubts.”

Thick algae layer

Banks warns to be cautious with water that’s pea-soup green, has a surface scum or a paint-like blue-green sheen, or clumps that look like spilled paint. “Rule of thumb: if you can’t see the bottom, keep people and pets out.”

Smell

Compared to green algae, which has a musty smell like that of a pond or damp forest floor, toxic algae smells putrid, like something is rotting. “It’s really gross,” says Huckstadt. “Don’t continue smelling it.” Paradoxically, adds Banks, a strong chlorine smell is also a red flag. The smell comes from chloramines — byproducts of the sanitation process — rather than from the chlorine itself. Rather than indicating there’s too much chlorine in the water, it means there isn’t enough.

Health Risks of Toxic Algae Exposure

Exposure to algae by itself isn’t a health risk, but exposure to the cyanotoxins from blue-green algae is. Skin exposure causes rashes, blisters and hives, and if you swim in the water, you could also suffer irritation of the eyes, nose or throat.

Ingesting affected water can lead to stomach cramps, nausea, diarrhea, and vomiting. “Just smelling the stuff can trigger respiratory problems,” warns Huckstadt.

How to Get Rid of Algae in a Pool

It isn’t easy. The pool experts we interviewed recommended slightly different procedures, but they all involved shocking the pool with a high enough dose of chlorine to kill the algae, scrubbing the bottom and sides of the pool, and filtering out the dead algae through the pool’s filtration system. Once the process is complete, which can take 24 to 48 hours, they recommended rebalancing the water chemistry to the proper pH, alkalinity, chlorine and free chlorine levels. Severe blooms may call for the addition of a algaecide to the pool water.

How to Prevent Algae From Coming Back

Algae thrives in warm, stagnant water with plenty of phosphates for food. To make the pool hostile to algae, Banks recommends circulating the water by running the pool pump for one hour each day per each 10 degrees (F) of outside temperature, which means eight or nine hours on a hot summer day. In addition, you should clean the filter regularly and keep the water balanced.

“While staying on top of sanitation is important, also making sure that the algae does not have a food source in your water, such as phosphates, is also very important. Algae has to have food to live on, which is why it’s critical to clean (vacuum and brush) your pool regularly.” Friedman adds that using a pool cover and keeping your pool at a cooler temperature are good preventative measures.

FAQ

Is the algae at the Lincoln Memorial Reflecting Pool toxic?

Banks says the Lincoln Memorial’s Reflecting Pool has prime conditions for toxic algae. “That’s shallow, untreated, sunbaked standing water — exactly the conditions cyanobacteria love,” he says. “So yes, a bloom like that can absolutely be toxic.” While there’s no way for him to say with any certainty that it is or isn’t toxic, he stresses “it’s not water anyone should be wading into.”

Huckstadt agrees with Falk, who says: “The Lincoln Memorial Reflecting Pool gets algae blooms on occasion and just needs to be treated. Not harmful to people unless it goes untreated and develops bacteria.”

About the Experts

• Graham Banks is a licensed Florida pool & spa contractor and the founder of Verify My Contractor, a free contractor license lookup site.
• Rafi Friedman is the president of Coastal Luxury Pool Builders in Nocatee, FL. The company services over 1,000 clients and builds over 100 pools annually.
• Randy Huckstadt, has 20+ years in the pool and HVAC industries and is a Contractor & Service Technician at JustAnswer.
• Brock Falk is a pool care field manager at Shasta Pools. He is based in Arizona.

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