The Lincoln Memorial Reflecting Pool: Why It’s Green and How to Fix It

It’s not every day that pool maintenance hits the national zeitgeist, but the algae bloom at the Lincoln Memorial Reflecting Pool has certainly done it. Lately, our social media has been flooded with (mostly tongue-in-cheek) requests to send a truckload of Yellow Treat to Washington, D.C.

It begs the question: what’s actually going wrong with the pool, and how do we fix it? Can a hefty dose of Yellow Treat save the day?

Definitely Not Your Backyard Pool

Let’s put things in perspective. The Lincoln Memorial Reflecting Pool is massive. Measuring 2,030 feet long by 167 feet wide, with an average depth of just 24 inches, it holds over 5 million gallons of water. That’s roughly 339 times the size of your average backyard pool!

Originally finished in 1922 using asphalt and tiles, it was completely rebuilt between 2010 and 2012 with concrete, making it function much like a giant in-ground pool. During that renovation, the water source was switched from city tap water to the local Tidal Basin (fed by the Potomac River). While drawing water from the basin saves millions of gallons of potable drinking water, it also introduces a steady stream of organic contaminants. To combat this, they added a dedicated internal circulation and filtration system equipped with ozonation.

Fast forward to more recently, when the pool received a “quick fix” for leaks and aesthetics: an epoxy coating painted “American Flag Blue.”

Designed for Aesthetics, Built for Algae

The reflecting pool has battled algae for a long time—even before the 2012 renovation. In fact, its very design practically guarantees an algae war.

First, there’s the sheer scale. Treating 5 million gallons is no small feat. Add to that a massive surface area and a shallow depth, and you’ve built the world’s most perfect algae incubator—especially under the hot summer sun. Toss in the local wildlife (ask any pool owner how they feel about ducks), and you’ve got a nutrient-rich soup. If you were trying to farm algae, you’d build exactly this pool.

The water source and drainage complicate things further. While the pool continuously circulates water through its own internal filtration loop, all 5 million gallons eventually have to go somewhere. Whenever the pool overflows due to heavy rain or is drained for its annual deep cleaning, the water discharges directly back into the Tidal Basin and the Potomac River.

Because of this direct link to the local ecosystem, chemical remediation is severely restricted by the EPA. Dump a persistent chemical in, and you pollute the river. That’s why the National Park Service currently uses hydrogen peroxide and ozone to oxidize the algae—they break down safely into water and oxygen, but they don’t stick around in the pool to keep it clean.

And then there’s that blue paint job. Intended as a cheap and fast aesthetic upgrade, the dark blue color absorbs more sunlight, further warming the shallow water. Worse, the epoxy coating is already delaminating (peeling), which just creates more crevices for algae to hide in.

Ultimately, this algae problem is the result of a series of compromises: a shallow design primed for algae, a natural water source rich in organic matter, and a dark, peeling paint job.

Cheap, Good, or Fast: Pick Two

You know the old project management triangle: “Cheap, Good, Fast – you can only pick two.”

• The original Lincoln Memorial project cost $3 million (about $60 million today) and took eight years. Good and maybe cheap, but definitely not fast.
• The 2010 restoration rebuilt the pool from the ground up for $30 million over two years. Good and fast, but not cheap.
• The recent blue epoxy renovation cost around $16 million and took just two months. Cheap and fast, but definitely not good.

The Triangle of Pool Sanitation

In the pool industry, we rely on the sanitation triangle: circulation, chemical treatment, and filtration. If one leg is weak, the other two have to work overtime, or things start turning green.

In a reflecting pool, circulation is deliberately kept low to prevent ripples. Chemical treatment is strictly limited to prevent pollution of the Tidal Basin during draining and overflow events. That leaves filtration doing almost all the heavy lifting—and it simply can’t keep up.

Could Yellow Treat Actually Fix It?

To answer our cheeky commenters: Yes, technically. If we sent roughly 200 lbs of Yellow Treat and shocked the pool with 500 gallons of liquid chlorine, it would eradicate the algae completely. (And hey, if the U.S. government wants to buy in bulk, we’re happy to offer a discount!)

It would be a fast, cheap fix. The pool might even stay clear for a week. But the algae would return. Why? Because the system’s underlying problems haven’t been addressed. And EPA doesn’t want massive amounts of chlorine and bromine compounds going into the Tidal Basin the next time it rains, or the pool needs to be drained.

Herein lies the Catch-22 of open-water sanitation: the very thing that makes a sanitizer environmentally friendly (like ozone or hydrogen peroxide degrading quickly) also means it has zero staying power. In a pool constantly bombarded by contaminants, you need a persistent sanitizer, such as stabilized chlorine, to keep algae at bay.

Some folks suggest phosphate removers. While controlling phosphates helps limit algae’s food source, it’s practically impossible to keep phosphate levels at zero in an open, 5-million-gallon body of water. You still need a persistent sanitizer.

No Easy Fix

So, how do we actually solve the Lincoln Memorial’s green problem? It’s going to take some serious infrastructure changes:

1. Go Back to Grey: As pretty as the blue might be, returning the basin to its original light grey will keep the water cooler and slow algae growth.
2. Fix the Water Source: Either massive upgrades are needed to pre-treat the Tidal Basin water before it enters the pool, or the NPS needs to install a robust remediation system to remove persistent sanitizers like chlorine just before the water discharges back into the river.
3. Beef Up Filtration: If chemical treatments remain limited, the filtration system needs a massive expansion to handle the heavy biological load.

These fixes are good, and they might even be fast, but none of them are cheap.

But maybe that’s the point. Monuments aren’t supposed to be cheap. They are massive projects designed to elicit awe, pride, and respect. You can’t get those things on the cheap. You only get them when you do it good.