Algae turns Trump's newly renovated Reflecting Pool green days after $14 million makeover

A quick bloom

Less than a day after the pool was refilled and unveiled on 4 June, algae began spreading across the shallow water, quickly replacing the intended “American flag blue” with a murky green. By Tuesday morning, dark clumps of algae sat on a lighter green layer that had blanketed the basin. The outbreak spread rapidly, defying an Interior Department pledge made the previous Friday to remove it using new nanobubble technology.

The reflecting pool is perfect for algae. If you were trying to biofarm algae, this would be the way to go. It's warm, it's stagnant, it's perfect.

A costly renovation

The Trump administration spent between $13 million and $14.2 million to drain, clean, resurface, and repaint the pool, awarding a no-bid contract to a company that had never worked for the federal government but had previously serviced Trump’s golf courses. The project was part of a broader push to refresh Washington monuments before the nation’s 250th anniversary celebrations on 4 July.

The National Park Service is actually maintaining the beautifully completed Reflecting Pool.

Blame and treatment

Officials attributed the bloom to residual algae in supply lines that sat dormant during the eight-week renovation, as well as the pool’s usual water source, the algae-prone Tidal Basin. Hot, stagnant conditions made the problem worse. To fight it, workers applied 12% hydrogen peroxide, a treatment milder than chlorine, and deployed high-tech nanobubble ozone systems from an Ohio-based contractor paid $1.7 million.

There's always going to be a rebound of the algae. Hopefully it works as a quick fix, but these algae do tend to rebound.

Heat and climate links

Scientists also pointed to broader forces. Hans Paerl, a former professor at the University of North Carolina, noted that rising global temperatures are expanding algal blooms worldwide, creating ideal conditions in shallow, still water bodies like the Reflecting Pool. Washington was bracing for hotter-than-normal weather later in the week, which risked making containment even harder.

It's clearly a temperature effect allowing them to optimize their growth.

A political setback

For the White House, the green-tinged water was a visible embarrassment ahead of Independence Day. Trump had promoted the renovation as a bargain solution that would keep the pool clean, but visitors arriving this week encountered a basin thick with algae. Tourists said they had heard reports of the problem but were surprised by its scale.