Hydrogen Peroxide in the Lincoln Reflecting Pool: A Chemical Clean-Up Under Scrutiny

Why the Lincoln Memorial Reflecting Pool Turned Green

The Lincoln Memorial Reflecting Pool has been a cherished symbol of American heritage for nearly a century. However, in recent days, the pool's surface has taken on an unexpected green hue, prompting concern among visitors and officials alike. This sudden change is attributed to an algal bloom that has rapidly spread through the shallow, slow-moving water.

The pool, which was recently renovated as part of President Donald Trump's preparations for the nation's 250th anniversary, had undergone a comprehensive overhaul in just weeks. The renovation included resurfacing and refilling with fresh water, potentially leaving behind residual algae in the pipes and systems while introducing warmed water during the early summer heat.

Algae blooms are not unprecedented at this location, as the pool's design—fed in part by the nearby Tidal Basin—creates ideal conditions for algal growth. But the speed of this latest bloom has drawn attention, raising questions about whether the renovation process may have contributed to these conditions.

"Given that a single cell can reproduce into millions within days, this is not viable to fully prevent," said Christopher Lowe, a marine biologist at Swansea University.

The challenge with algae blooms lies in their ability to grow quickly under certain conditions—namely sufficient light and nutrients. While sunlight cannot be controlled outdoors, nutrient levels can be managed, yet in the case of the Lincoln Memorial Reflecting Pool, these elements have combined in a way that has resulted in a visible algal bloom.

Why Hydrogen Peroxide Is Being Used

In response to this growing concern, officials have opted to use hydrogen peroxide as part of a dual approach to treating the algae. This chemical is being applied alongside nanobubble ozone systems designed to kill algae and pathogens throughout the water column.

Hydrogen peroxide is a common oxidizing agent used in water treatment facilities to break down organic contaminants, including algae. It is considered milder than chlorine and has been widely used in natural swimming pools and similar environments where wildlife is present.

Steve Goodale, known online as "Swimming Pool Steve," explained that hydrogen peroxide works in tandem with other systems already in place:

"Adding peroxide is, in effect, doing the same thing that the nanobubbler system does—oxidation of the organic debris. So they do not need to add enough peroxide to combat the algae entirely, just enough to help support the ozone nanobubblers."

However, effectiveness depends heavily on conditions inside the pool, including algae density and debris levels. For a body of water as large as the Lincoln Memorial Reflecting Pool—holding roughly 6.5 million gallons—the challenge of treating it effectively at scale presents significant logistical issues.

Problems With Using Hydrogen Peroxide

1. The Sheer Scale Problem

The sheer volume of water in the pool makes the application of hydrogen peroxide a daunting task. According to Goodale, estimating the required dose is inherently difficult without knowing the extent of contamination.

"The amount of peroxide needed depends not just on the strength concentration… and the size of the body of water, but also importantly the amount of algae and physical debris in the water," he said.

He offered a rough estimate: "As a rough number—something in the order of 2,000 gallons of 12 percent peroxide would be needed to effectively treat the 6.5 million gallons." Videos show workers manually pouring containers of 12 percent hydrogen peroxide into the pool from the edge, but treating a body of water that size would typically require far larger quantities.

"Dosing for a system this large would normally happen in the filtration equipment area. It would definitely not be standard protocol to manually treat a body of water this large," Goodale noted, suggesting that using 1-gallon jugs is likely an insufficient measure for such a vast volume.

2. Cost vs. a Short-Term Fix

Hydrogen peroxide is effective in the short term, but it is not a permanent solution. Because it breaks down rapidly into oxygen and water, it does not remain in the system long enough to prevent future growth.

"The hydrogen peroxide only works in the very short term," said Lowe.

This raises questions about cost-effectiveness. Treating a pool of this size at sufficient concentrations—and repeating that process as algae returns—could run into significant expense, especially when compared with longer-term fixes focused on nutrient control and circulation.

3. A Design Trade-Off: Still Water vs. Circulation

The reflecting pool's design has long been a balancing act between aesthetics and water quality. Algae thrives in warm, slow-moving water, conditions that are required for the mirror-like surface the landmark is known for.

While increased circulation or aeration can help reduce algal growth, it can also disrupt reflections. Experts say managing the pool therefore becomes a balancing act between aesthetics and water quality—one that has challenged multiple renovation efforts over decades.

The recent overhaul may have altered how heat and nutrients behave in the system, potentially accelerating bloom conditions. Goodale said recent weather and design changes may be contributing factors:

"This is definitely a reactionary approach to trying to prevent the algae from getting worse—which it will quickly with warm weather, lots of rain, and the new darker interior surface absorbing more heat from the sun," he said.

4. Wildlife and the Wider Environment

The reflecting pool is not an isolated system. Birds, debris, and runoff all interact with the water daily. While the chemicals being added to the water will remove the algae in the pool, because of the dilution ratios used, they should not pose a risk to wildlife or humans nearby.

"The peroxide itself is being diffused into such a large body of water that the concentrations should not be harmful," said Goodale. "Hydrogen peroxide is a good choice here, leaving only water and oxygen, neither of which should be harmful to local wildlife."

However, there are ecological trade-offs to repeated chemical control. While hydrogen peroxide is generally considered less harmful than chlorine and breaks down into non-toxic components, maintaining the pool through continuous dosing could limit what plants and other matter can survive in the water.

"The hydrogen peroxide should have minimal impact on the wider environment, but his will essentially mean that from the standpoint of nature the pool will be an ecological desert with nothing being able to live in the water," Lowe said.

Conclusion

The ongoing treatment of the Lincoln Memorial Reflecting Pool represents a complex challenge at the intersection of environmental science, public aesthetics, and historical preservation. While hydrogen peroxide is seen as a safer alternative to traditional chlorination methods, its application at such scale presents both logistical and sustainability concerns.

As officials continue to monitor the situation and implement solutions, it becomes clear that this case study may serve as a precedent for future management strategies in similar water features across the nation. The careful balance between maintaining historical integrity and ensuring ecological responsibility will remain paramount as we look toward long-term solutions.