Why Is the Lincoln Memorial Reflecting Pool Turning Green?
The Lincoln Memorial Reflecting Pool in Washington, D.C., has turned green after being refilled with water following a $14 million renovation, sparking questions about the project’s outcomes and algae management. The pool’s bottom, repainted “American flag blue” during the Trump administration, was refilled in early June 2023, but within days, algae blooms transformed the water into a vivid green. Experts attribute the phenomenon to a combination of environmental factors and the renovation’s impact on the pool’s ecosystem.
According to the National Park Service (NPS), the algae bloom is a natural occurrence known as “New Pond Syndrome,” where stagnant water in open environments quickly develops algae. Steve Goodale, a swimming pool specialist and self-described “Swimming Pool Steve,” explained that the pool’s size—2,030 feet long and 338,000 square feet—delayed the algae growth but did not prevent it. “It’s a known issue when you restart a large body of water,” he said. NPS officials confirmed the algae is non-toxic and belongs to the genus *Desmodesmus*, a common species in the region.
What Are the Experts Saying About the Algae?
Rosalina Stancheva Christova, a professor of aquatic ecology at George Mason University, analyzed water samples from the pool and confirmed the algae’s presence. “The conditions are ideal for *Desmodesmus*: shallow, stagnant water with strong sunlight,” she said. Christova noted that the 2023 renovation may have disrupted nutrient balances, accelerating the bloom. She also pointed to the pool’s design as a contributing factor. “It’s essentially a manmade shallow lake, and algae thrives in such environments,” she added.
The Trump administration attributed the algae to “residual material in supply lines” and cited extreme temperatures—heat index values exceeding 95°F—as exacerbating the issue. However, Interior Department officials acknowledged the pool has faced algae problems since its 1922 completion, with previous incidents requiring draining and ozone recalibration. The 2012 renovation, for example, led to similar blooms, according to NPR reports.
How Is the Government Addressing the Algae Problem?
To combat the algae, the Interior Department is using hydrogen peroxide and “nanobubble ozone technology,” a method described as safer than chlorine. The agency claims the approach is validated by universities and the National Oceanic and Atmospheric Administration (NOAA). “The nanobubbles are neutrally buoyant and can last weeks, oxidizing algae and pathogens,” said Goodale, who reviewed the technology’s efficacy.
Workers have deployed ozone machines and vacuum systems to remove dead algae, but as of late June, much of the pool remained green. Loay Hidmi, a water treatment engineer monitoring the site, estimated the cleanup was 80% complete but warned the algae could return due to the pool’s favorable conditions. “It’s an aesthetic concern, but it raises questions about long-term maintenance,” he said.
What Does This Mean for the Reflecting Pool’s Future?
The renovation, initially budgeted at $2 million, ballooned to $14 million, with $1.7 million allocated for nanobubble technology alone. Despite the upgrades, the pool’s underlying issues—such as aging pipes and leaks—remain unresolved. A 2023 Interior Department report highlighted the need for improved filtration systems, but the latest project focused on resurfacing and sealing, not structural repairs.
Christova urged weekly water monitoring to track algae growth and prevent harmful species from taking hold. Meanwhile, the White House credited the renovation with “permanently sealing” the pool, though critics argue the fixes address symptoms, not root causes. As the National Mall prepares for 2026’s semiquincentennial events, the reflecting pool’s green hue underscores the challenges of preserving historic landmarks in a changing environment.