The Lincoln Memorial Reflecting Pool in Washington, D.C., has once again turned green, a recurring challenge rooted in its original design and location. Built atop a former marshland drained and paved over, the shallow, nutrient-rich basin has long provided ideal conditions for algal blooms, despite repeated chemical treatments and maintenance efforts.

The pool, situated between the Lincoln Memorial and the Washington Monument, was constructed on dredged Potomac marshland and faced structural and water quality issues from the outset. Leaks and settling led to frequent water loss, and subsequent renovations—including a 2012 refurbishment that made the pool shallower and changed its water source to nutrient-rich water from the Tidal Basin—have inadvertently exacerbated algae growth. In recent years, efforts such as adding hydrogen peroxide or altering the pool’s color to a darker “American Flag Blue” have failed to prevent recurring algal blooms.

Experts note that algae thrive under the pool’s conditions: warm, shallow waters rich in nitrogen and phosphorus. Algal cells reproduce rapidly, and chemical treatments often worsen the problem by releasing nutrients back into the water, fostering further growth, according to University of Maryland phytoplankton ecologist Pat Glibert. “You’re fighting a losing battle,” Glibert said, emphasizing the repeated struggles of federal managers over the past century.

Some specialists advocate for a paradigm shift, suggesting that restoring natural wetland ecosystems would provide a more sustainable solution. Such systems employ a combination of running water, gravel, plants, and biofilms of microorganisms that absorb excess nutrients, thereby limiting algal proliferation. This approach, long used in natural swimming pools and ponds worldwide—from Minnesota to Europe—could reduce chemical use, energy consumption, and maintenance needs while producing clearer, healthier water.

James Robyn of BioNova, a company specializing in natural-pool systems, explained that the key is not eliminating algae entirely but preventing conditions that enable blooms by cutting off nutrient supplies. BioNova and other innovators propose incorporating biofilters—engineered wetlands with aquatic plants and substrates—or bioreactors with gravel layers coated by nutrient-consuming microbial biofilms. Such designs mimic natural environments, potentially transforming the Reflecting Pool into a “Reflecting Swamp” that combines historical aesthetics with ecological function.

However, the scale and context of the Reflecting Pool present unique challenges. The basin holds roughly 6.8 million gallons of water, making it far larger than typical natural pools. Designers must also contend with external factors like water from the Tidal Basin, summertime heat, and contaminates such as bird droppings. Moreover, any modifications must maintain the pool’s reflective qualities, which are integral to its symbolic and visual purpose.

Cost estimates for such a transformation are not precise but would likely run into the tens of millions of dollars, outstripping recent surface treatments like the Trump administration’s $14 million paint job. Proponents argue that, while the investment would be substantial, it could yield long-term savings by reducing ongoing chemical treatments and maintenance.

Despite this potential, the U.S. Interior Department has not indicated any openness to considering natural filtration methods for the Reflecting Pool. Experts see the issue as emblematic of broader governmental struggles with long-term environmental planning, where quick fixes often replace sustainable solutions.

As algae continue to reclaim the pool, some ecologists and engineers suggest that embracing nature’s own systems offers a way forward. Restoring a wetland-like environment beneath the capital’s iconic monument could not only resolve the persistent water quality problems but also symbolize a new commitment to working with natural ecosystems instead of against them.