Donald Trump has blamed “vandalism” for “real problems” at Washington’s reflecting pool after an algae bloom in the wake of a $14.2m renovation of the site he declared would turn it “American flag” blue. Paint has also been seen peeling off in the water.

Days after his administration claimed the pool was actually “crystal clear”, despite an unmistakably green hue, the US president acknowledged issues – and, without evidence, blamed foul play.

“We’ve cleaned, renovated, and beautified over 45 Monuments and Memorials, 28 Statues, and 22 Fountains in Washington, DC,” Trump wrote in a lengthy post on his Truth Social platform on Friday night. “However, we’ve had some real problems with Vandalism at the beautiful Reflecting Pool, which sits between The Washington Monument and The Lincoln Memorial.”

He noted that “86 47” was recently etched onto a vast patch of grass nearby – “86” is frequently used across the restaurant industry to mean “stop” or to get rid of something, while Trump is the 47th president of the US – and claimed some people had “also done everything possible to hurt the inside surface” of the pool painted as part of the recent renovation.

“No different than the chemicals that were used on the National Mall, they used something similar in the Reflecting Pool to try to destroy and demean our beautiful work,” Trump alleged, again without evidence.

Trump also claimed in his post that the algae problem was largely under control, suggesting it was “75% gone” and the issue would soon be “completely remedied”.

Law enforcement is “actively investigating this situation”, he claimed, and “will hopefully have it resolved soon”. The Department of the Interior did not immediately respond to a request for comment regarding Trump’s statement.

Trump ordered a refurbishment project to turn the pool “American Flag blue” ahead of the country’s 250th birthday celebrations. The site – one of Washington DC’s most historically symbolic attractions – has been one element of his efforts to recondition Washington during his second term.

Just days after the renovation was finished, however, an algae bloom turned the water green. In response, National Park Service employees were deployed and seen using skimmers and adding hydrogen peroxide to the water in an attempt to restore the water quality.

In a statement on social media on Wednesday, the interior department declared that “advanced nanobubbler technology” had “very effectively killed the algae”, adding: “Our National Park Service team is now vacuuming up the dead algae resting on the bottom of some parts of the Reflecting Pool – just like the destroyed Iranian Navy resting on the bottom of the Persian Gulf.”

In reality, however, much of the water remained murky later in the week, with algae still visible in some areas, and large flakes of paint peeling from the basin and floating on the surface.

The Atlantic reported this weekend that laboratory testing it commissioned identified algae in the pool as Scenedesmus, a genus of green algae.

The project has also come under scrutiny over its contracting process. The New York Times reported that the Trump administration had awarded a no-bid contract to a business tied to a longtime supporter of the president to install the water-purification system in the pool.

Tim Walz, the Minnesota governor who ran against Trump and JD Vance as the running mate of Kamala Harris in the 2024 presidential election, wrote on X, formerly Twitter: “Found an imaginary problem, said only they could fix it, didn’t listen to experts, hired buddies who grifted millions, failed miserably, bragged how great it went. The entire Trump presidency in a nutshell.”