Reflections on the Algae in the Lincoln Memorial Pool

“About two-thirds of the oxygen in our atmosphere is produced in the surface waters of the sea by phytoplankton, the minute forms of algae that give the sea it’s slightly green hue, and which initiate the entire food web for the ocean.”

Jacques Cousteau, pioneering French oceanographer

“No matter how politely one says it, we owe our existence to the farts of blue-green algae.”   Diane Ackerman, American poet and naturalist

Recently, the algae in the Lincoln Memorial Reflecting Pool in Washington, D.C., became a national news story and the pool “bloom” a major tourist spectacle. When I first learned of it, I wondered what species of algae was growing in the pool, and whether it posed any threat to the public or was just another costly blight on our nation’s capital. As the focus of Germ Gems is on the microbial world, this week’s post is primarily on the microscopic, not the wider (political), ramifications of this unwanted algae “bloom.”

What are algae and how do they differ from cyanobacteria (aka “blue-green algae)? Algae (from the Latin alga) are a variety of eukaryotic (nucleated) organisms, most of which live in water and carry out photosynthesis, producing about half of the oxygen in the Earth’s atmosphere. The ancient Greeks and Romans knew of algae, but it wasn’t until the late 19^th and early 20^th century that phycology (the scientific study of algae) became recognized as a field. (By 2023, phycological funding reached nearly 1 billion USD.)

True algae—eukaryotes that perform oxygenic photosynthesis—are formally classified into several divisions (phyla) based, in large part, on their pigmentation. The most prominent are: Chlorophyta (Green Algae), Rhodophyta (Red Algae), Phaeophtya  (Brown Algae), Chrystophyta (Golden-Brown Algae), Dinoflagellata (Fire Algae, cause of red tides), and Euglenophyta (Euglenoids).

Most algae are beneficial and essential to life on Earth. They are the base of the food web and provide energy to most aquatic life: these are critical ecological functions. If all algae suddenly disappeared, most aquatic systems—and ultimately much of life on Earth—would collapse.

In addition, the value of algae spans global markets with highly potent nutritional and medical applications. The global algal nutraceutical and pharmaceutical market alone is projected to reach over 1 billion USD by 2027. The medical and pharmaceutical value of algae is centered, in the main, in cardiovascular health and as anti-inflammatory agents.

Most algae are not health risks. They can, however, be a nuisance if they “bloom” (grow rapidly). 

Cyanobacteria, on the other hand, can not only be a nuisance and unappealing to look at—the blooms have the appearance of blue-green paint—but, they can also be toxic. Several genera of Cyanobacterium can produce toxins that affect the nervous systems and livers of both humans and animals.

Cyanobacteria are often referred to as Blue-Green Algae because they contain a blue pigment.  They are not, however, algae; they are prokaryote bacteria and like all prokaryotes lack a nucleus.

And, they are ubiquitous. Cyanobacteria can be found in almost every terrestrial and aquatic habitat—ocean, fresh water, damp soil, and bare rocks (even rocks in Antarctica). 2.4 billion years ago, the release of a massive amount of oxygen from cyanobacteria-- the “Great Oxygenation Event”—made life on Earth habitable for aerobic organisms like us.

What’s in the pool? The makeover of the Lincoln Memorial Reflecting Pool was supposed to inspire patriotism. (Kovac, A., “Why is the paint peeling off the Lincoln Memorial Reflecting Poole? An investigation,” Scientific American, June 22, 2026). It has fallen far short of that goal.

Recently, scientists identified the algae flourishing in the reflecting pool as Scendesmus, a genus of green algae nicknamed by scientists the “Skinny Dead Mouse.” (Viser, M., “Science Has a Name for What’s Plaguing the Reflecting Pool,” The Atlantic, June 19, 2026). This freshwater green alga is found worldwide in ponds, lakes, reservoirs, and slow-moving water. Fortunately, Scenedemus is considered a nuisance rather than a major public health hazard.

Nonetheless, we are now faced with the cost of cleaning up  this algae “bloom”—one of the largest recorded in recent years. And, to date, the reflecting pool’s restoration project has already cost the American public well over 15 million dollars.

I don’t think anyone would disagree that the emergence of the algal bloom in the Lincoln Memorial Reflecting Pool is the result of many mistakes. But, as the American industrialist and business magnate Henry Ford once said: “The only real mistake is the one from which we learn nothing.”  Let’s hope those in charge take advantage of this robust learning opportunity. Afterall, no irreversible harm has been done and for that we should all be grateful.