The Lincoln Memorial Reflecting Pool has turned a murky green, and the scientists who study algae say they aren’t surprised – the pool’s own design practically invites it.
Algae blooms hit the pool in the summer months with some regularity, but the timing of this outbreak has drawn attention because it followed a recent renovation. Experts told NPR the renovation may have helped speed the growth along, though the shallow, sun-soaked water is the core problem. Shallow water warms fast. Fast-warming water is exactly what algae wants.
Why the pool stays green
The Reflecting Pool stretches nearly 2,000 feet between the Lincoln Memorial and the Washington Monument – a broad, open basin that gets direct sunlight for most of the day. Shallow depth means there’s little cold water below to keep surface temperatures in check. That combination, scientists say, creates near-ideal conditions for algae once summer heat sets in.
Renovation work can stir up sediment and shift the nutrient balance in a body of water, giving algae an early advantage over whatever organisms might otherwise compete with it. NPR reported that experts believe the recent overhaul at the pool likely contributed to the accelerated growth seen this summer.
Algae itself isn’t unusual in open freshwater. What made this instance visible enough to draw public comment was the pool’s profile – it sits at the center of the National Mall, a backdrop for ceremonies, protests, and the kind of public gatherings the Trump administration has tied to it in recent months.
The pool gained renewed attention after plans connected to administration events placed it front and center. Green water wasn’t the backdrop anyone had in mind.
NPR didn’t report on any immediate remediation timeline, and it’s not clear when – or whether – crews plan to treat the water before any scheduled events at the Mall.
Reporting by NPR, published June 19, 2026. Read the original report.
