Growing Algae in Front of President Lincoln

The Iconic Washington Water Feature

In Washington D.C. between the National Monument and the Lincoln Memorial is the 2,030 foot long Reflecting Pool. Built in 1923, the pool was designed to be a giant water mirror to reflect both the National Monument and the Lincoln Memorial. It has served as an iconic vision in many Hollywood movies such as Forrest Gump, Spiderman: Homecoming, and Captain America: The Winter Soldier. The pool is also famous for being the site of the civil rights rally in 1963 where Martin Luther King Jr. gave his I Have a Dream speech. More recently, the Lincoln Memorial Reflecting Pool has become famous for something else: Algae.

My Personal Revelation

It was a hot and humid September day in 2016. I was going to visit the National Mall in Washington, D.C. for the first time. When I arrived, I was excited to see the Lincoln Memorial and the Reflecting Pool. When I got to the pool, I was shocked at what I saw and smelled. The water in the pool was dark green with huge plumes of algae beneath the surface. And there were mats of scum floating on the top. The air around the pool smelled like a dead fish. It was gross for a national monument. As I continued towards the Lincoln Memorial and up the famous steps,I kept thinking about the reflecting pool. I entered the memorial and was awed by the 19-footmarble statue of Abraham Lincoln and the words of the Gettysburg Address inscribed on the walls. I stood for a long time in silence, soaking in the vibe of the place. Then I headed back towards the reflecting pool. While coming down the steps to look again at the massive pool with 6.75 million gallons of algae laden water I stopped suddenly and said aloud to myself, “This isn’t a pool, it's just a great big pond.”

And The Algae Still Keeps Growing

Fast forward to June 2026 and the Lincoln Memorial Reflecting Pool has become famous again. Not for being in a movie or the site of some historic event. No, the reflecting pool has become famous once again for growing algae. I was invited to be interviewed on a podcast regarding the algae in this legendary venue. Since I have worked in the swimming pool industry for over 40 years, I do know a thing or two about water and algae. Prior to appearing on the podcast, my thoughts rushed back to when I was there in 2016. Again, what resonated with me was the thought that this is not a pool; it is a big pond. That led me to decipher just what the differences are between a pool and a pond.

The Difference Between a Swimming Pool and a Pond

The first thing to consider since algae would be the focal point of this interview is to express what kind of environment algae needs to grow. Everything algae needs can be found in most bodies of water and that includes swimming pools. For algae to be comfortable it needs to sustain itself. One main way in which this is done is by photosynthesis or the ability to use sunlight to convert water and carbon dioxide into oxygen and carbohydrates. Algae can create their own energy and fuel for growth from light.

Then there are nutrients like phosphate and nitrates. Dissolved carbon dioxide is in water as welland much needed by algae. Other contributors in all water can include calcium, magnesium, sodium, potassium, and sulfur (sulfites). Even small levels of metals like copper, manganese, cobalt, and zinc in water can act as micronutrients to algae. All these growth ingredients can be found in swimming pools and ponds. The difference with a swimming pool is that it is the intentional design and maintenance of swimming pools to prevent the excessive growth of algae. Swimming pools are designed to have a highly active movement of the water from circulation. Moving water is healthy water. Pools are also designed with efficient filters to remove small particles and keep the water clear. And the chemistry of pools is designed to keep the water clear and free of bacteria and algae by using disinfectants like chlorine and additional water treatment devices like ozone and ultraviolet UV. Ponds on the other hand are designed to be slow intentionally quiescent with little to no filtration. This is certainly the case with the Lincoln Memorial Reflection Pool. It was intentionally designed to be a very still “water mirror.”

Nutrients Plus Light and Heat Equal Algae

Since the main source of water to the Lincoln Memorial is from a tidal basin reservoir, the water is heavy with nutrients. The 0.3-mile-long reflecting pool is shallow and sits all day long under direct sunlight. It wasn’t until a major reconstruction project between 2010 and 2012 that circulation and filtration were introduced, and even more recently—in the summer of 2026—an ozone 'nano bubbler' system was deployed in an attempt to combat severe algae blooms following the resealing of the pool surface. While the upgrades may or may not help they are not similar to the way a pool circulates and filters. Swimming pools have strong consistent movement of the water and submicron filtration for removal of contaminants. While algae may be minimized from the current upgrades to the reflection pool it is most likely it will never be completely eradicated due to the still shallow water under lots of sunlight. Another consideration is the temperature. Algae love warm water and proliferate in growth under hot and humid conditions, like Washington DC in the Summer and Fall. Lastly, the Lincoln Memorial Pool has never incorporated one of the best algaecides well known to swimming pool professionals. That is the use of chlorine at proper levels. Chlorine when dosed and managed correctly in water is one of the most effective algae killers and preventors. The managers of the Lincoln Memorial Pool have also incorporated the use of hydrogen peroxide along with the nano-bubbler. This theoretically produces hydroxyl radicals which are powerful destructors of undesirable microorganisms like algae. There are varying opinions as to the effectiveness of this process. It should be noted however that ozone and UV have been secondary disinfectants designed to be used with a minimal amount of chlorine sanitizer in recreational water for decades.

Let’s Be Honest About What the Reflection Pool Really Is

The proof will be in the pool or pond as to the results of the 16 million dollar refurbishing of the surface and the added technology. It is this pool pro's opinion, however, that a simple name change may also help change viewpoints and treatment of this troublesome liquid memorial. It is not and cannot be treated like a swimming pool. My proposed change is to call it what it is. The Lincoln Memorial Reflecting Pond. After all wasn’t President Lincoln also known as Honest Abe?