Trump wanted the Reflecting Pool to be ‘American flag blue.’ Algae is turning it green.

The Trump administration has spent millions renovating the Reflecting Pool on the National Mall to make it “American flag blue” in time for the nation’s 250th anniversary celebrations.

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But even faster than it was repainted, the water has turned to a dark green — thanks to algae growth.

The new hue comes despite significant cost and controversy, and is something of a stumble after boasts by President Donald Trump about how he was able to make the famous landmark look so much better than his predecessors did. Last month, he drove over the Reflecting Pool as it was under construction, boasting about the beautiful blue color it would be.

“It never had the color people wanted, but now it’s going to have the great color,” he said at the time.

But after last weekend’s hot weather, D.C. residents began to notice that the pool had turned green.

Reached for comment on Tuesday, a spokesperson for the Interior Department continued to use the pool to mock Trump’s predecessors. “Unlike under Obama and Biden, the National Park Service is actually maintaining the beautifully completed Reflecting Pool,” the spokesperson said.

The spokesperson said that the National Park Service was using “high-tech nanobubble ozone technology” to kill algae, pathogens and contaminants.

“Additionally, hydrogen peroxide, which is a milder treatment than chlorine and is used in spas and specialty pools like natural swimming pools, is also treating the pool,” the spokesperson said. “There are no harmful side effects to marine life or to the environment.”

Shallow manmade bodies of water like the Reflecting Pool are prone to algal growth because they are warm, exposed to the sun and often filled with nutrients . Nutrients like nitrogen and phosphorus can spur algal blooms, according to the Centers for Disease Control and Prevention . These nutrients are contained in animal poop, like geese and ducks, which often spend time near the pool, and fertilizer, which is often transported by runoff after rainstorms.

Algae convert sunlight to chemical energy through photosynthesis, which allows them to grow and multiply. The shallow, broad footprint of the Reflecting Pool means that the organisms in the pool get plenty of sunlight, fueling growth.

Just days before the pool turned green, Trump had been celebrating the completed paint job on the popular tourist destination, saying in a Truth Social post that the pool’s surface was now a “very complex, but powerful, Dark Blue.”

He also has repeatedly touted various D.C. beautification projects, saying last week, “We did a hell of a job.”

“But everybody’s looking at that Reflecting Pool,” he said last week in the Oval Office, saying that the project cost around $10 million. “They can’t believe it reflects. We used a dark blue, it’s called American flag blue.”

The cadence of D.C.-area renovations — as well as Trump’s focus on them — has ramped up as the country approaches its 250th anniversary, which will be commemorated with a string of events in the nation’s capital.

Interior Secretary Doug Burgum has joked that he has become Trump’s “pool guy.” Trump also repeatedly criticized former Presidents Barack Obama and Joe Biden when he shared details about the Reflecting Pool renovation, saying in a Truth Social post that the pool “looked terrible” under the Democratic presidents.

Despite the water’s noticeable change, the White House touted the Reflecting Pool in a Monday post, sharing a picture of the water being blue. At the time of the post, the water was green.

“Making D.C. safe and beautiful again one cleanup at a time,” said the post.

Trump had touted the repainting of the Reflecting Pool ahead of the country’s 250th anniversary events, saying he wanted the beautification efforts in D.C. to be completed by July 4.

The project, like many of Trump’s efforts to reshape D.C., faced controversy and legal pushback.

The New York Times reported that the government is paying more than $13 million through a no-bid contract to a company that has performed work at Trump National Golf Club in Sterling, Virginia.

Questioned during a congressional hearing about reports on the contract, Burgum told lawmakers that he was “positive that we followed all of the required bidding rules.”

The project also faced pushback from the Cultural Landscape Foundation, which sued the Trump administration in May to try to block the reflecting pool from being repainted. “The dark grey, achromatic basin was not incidental to the design. It was the design,” wrote Alexander Kristofcak, an attorney for the plaintiffs.

The reflecting pool marks just one of a series of changes the president is pushing across D.C., including restoring fountains and adding a new surface to the World War II memorial fountain, Trump has said.

At the same time, he spearheaded the controversial ballroom project, including the demolition of the White House’s East Wing. The project faces a litany of criticism and legal challenges from critics and preservationists.

The president is also pushing for the construction of a 250-foot arch near the Potomac River. That project, too, has prompted legal challenges from veterans and historians.