Lincoln Memorial Reflecting Pool Is Now Green: 4 Possible Reasons

A multimillion-dollar renovation of the Lincoln Memorial Reflecting Pool-designed to give the historic landmark a deeper "American flag blue" finish-appears to have had an unintended consequence: the water already looks green.

Images of the pool from the last few days show algae spreading across the surface just days after the pool was refilled, raising questions about whether the redesign has altered conditions in ways that favor rapid blooms.

The overhaul, ordered by President Donald Trump as part of a broader effort to revamp the National Mall ahead of the U.S. 250th anniversary, involved resurfacing the century-old pool with a dark blue coating intended to improve its appearance and seal leaks.

While Trump had suggested the project would cost between $1.5 million and $2 million, federal records show contracts ultimately reached roughly $14 million. The work was awarded via a no-bid contract that has come under scrutiny and prompted a lawsuit from preservation group The Cultural Landscape Foundation, which argues the changes were carried out without required historic review.

A Historic Pool With Long-Standing Algae Problems

Stretching more than 2,000 feet between the Lincoln Memorial and the Washington Monument, the reflecting pool has been a defining feature of Washington, D.C. since 1923.

But algae blooms are not new. The shallow, slow-moving water has long been prone to appearing green in summer, particularly when heat, sunlight and stagnant conditions combine.

The issue has persisted even after major upgrades. In 2012, following a $34 million renovation, algae appeared within weeks of the pool reopening-prompting crews to drain and clean it again as officials worked to recalibrate the water treatment system. Algae returned quickly after that overhaul too, underscoring how difficult it is to fully eliminate blooms in a shallow, outdoor system like the reflecting pool.

Why The Algae Could Have Appeared

There are several possible explanations have been put forward for why the reflecting pool has turned green so quickly.

1. Residual Algae From the Renovation Process

An Interior Department spokesperson told Politico that the current algae is "residual," after supply lines sat dormant for eight weeks during construction-suggesting at least part of the bloom may be a routine post-renovation effect rather than a completely new issue.

2. The Darker ‘American Flag Blue’ Coating

The timing-just days after the pool was refilled-has prompted debate over whether the darker coating could be playing a role.

Darker surfaces absorb more sunlight and heat than lighter ones, which in shallow water can raise temperatures and increase the energy available for algae growth-potentially accelerating reproduction rates.

Alla Silkina, an algal biotechnology expert at Swansea University, explained that darker surfaces could contribute to conditions that favor growth, but stressed that other factors are typically more important.

"Darker surfaces can absorb more solar radiation and increase local water temperatures," Silkina told Newsweek. "This may create more favorable conditions for algal growth, although nutrient availability, water residence time, and species composition are often the primary factors controlling bloom development."

3. Weather and Environmental Conditions

Weather conditions may also be contributing. Warm temperatures, strong sunlight and relatively still conditions are well known to encourage algae growth, particularly in shallow, slow-moving bodies of water like the reflecting pool.

Silkina explained that these conditions can rapidly accelerate growth in the right environment.

"Light provides the energy for photosynthesis, while temperature influences metabolic and growth rates," she said. "In shallow water, greater light penetration and warmer temperatures generally promote faster algal growth, provided nutrients are available."

She added that nutrients remain a key limiting factor. "Even with favorable light and temperature conditions, blooms are unlikely to develop if essential nutrients such as nitrogen and phosphorus are limited," Silkina said.

4. Water Flow and Underlying Infrastructure

Some reports have also pointed to longer-standing infrastructure challenges beneath the pool, including issues with circulation or aging pipe systems.

If water movement or filtration is reduced, conditions can become more stagnant-making it easier for algae to grow and accumulate.

"Water circulation can significantly reduce bloom development," Silkina said. "Continuous mixing and flow prevent algae from accumulating in one location… visible blooms are less likely to appear rapidly in well-circulated waters."

Why It Looks Green

The green color itself is caused by chlorophyll-the pigment algae use for photosynthesis. As algae multiply, they begin to dominate how light is absorbed and reflected in the water, overpowering the underlying blue coating and shifting its appearance from deep blue to green.

Silkina noted that under the right conditions, this visual change can happen quickly.

"Under ideal conditions algal populations can double within hours to a few days," she said. "Visible blooms may develop within several days to one or two weeks, depending on the species and environmental conditions."

A ‘Perfect Storm’-and Unproven Claims

Taken together, these elements-residual algae, heat absorption, favorable weather and water flow-can create what scientists often describe as a "perfect storm" for rapid blooms rather than a single clear cause.

Alongside these explanations, some social media users have speculated-without evidence-that the situation could be the result of deliberate interference.

Figures including radio host and MAGA supporter Grant Stinchfield suggested the pool was "sabotaged" by Democrats, while author and Trump supporter Juanita Broaddrick wrote on X: "It appears very evident that the reflecting pool has been sabotaged. The left is evil."

There is no public evidence to support those claims, and officials have not indicated any foul play.

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This story was originally published June 15, 2026 at 9:35 AM.