The Lincoln Memorial Reflecting Pool ‌in Washington, DC has turned green with algae just weeks after it underwent a major multimillion-dollar renovation to make it shine an “American flag blue” colour.

On Friday, US President Donald Trump said on his Truth Social platform that the site had been vandalised, suggesting damage was done by “radical left lunatics”, but that the algae that had appeared was being cleaned up.

“We’ve had some real problems with Vandalism at the beautiful Reflecting Pool,” Trump said.

“The algae is 75% gone, and the condition will soon be completely remedied, and the area that was vandalized, fortunately, is just a small area of damage, and will be fixed early next week.”

Trump, however, did not provide evidence to support his allegation of vandalism, which he said included someone pouring corrosive chemicals into the pool.

Here’s what we know:

What has happened to the pool?

The Lincoln Memorial Reflecting Pool, which was constructed in 1922, is near the Lincoln Memorial where Martin Luther King Jr delivered his “I Have a Dream” speech in the United States capital in 1963.

The bottom of the pool has been repainted in ‌a colour Trump ⁠calls “American flag blue”, and on June 6, he announced the renovation work for the project, which cost  $14.7m, was complete.

But last week, the blue material at the bottom of the pool began peeling off – with parts of it seen floating on top of the water – and the water had turned verdant with algae.

Since June 16, US National Park Service work crews have been pouring hydrogen peroxide into the pool to combat the algae bloom.

A spokesperson ⁠for the Interior Department told Reuters that the pool is being treated with “high-tech nanobubble ozone technology” that kills algae, pathogens including E. coli, and other contaminants. The department added that the hydrogen peroxide also being used is “a milder treatment than chlorine” that is used in swimming pools.

Why is Trump claiming sabotage?

With the water in the reflecting pool having turned a visible green, on Friday, Trump claimed the site had been vandalised and wrote on his Truth Social platform: “Just like three days ago, they destroyed the grass outside of the Pool, they’ve also done everything possible to hurt the inside surface that was just installed.”

On Saturday, he said National Park Police “have arrested multiple individuals for vandalizing our Nations magnificent Reflecting Poll”, correcting his spelling to “Pool” later.

He went on: “Who would do such a thing? These are very serious crimes having to do with the destruction of National Monuments. Years in jail!”

One man arrested was David Hearn, 67, of Bethesda, Maryland, who owns a company making composites that are used to build watercraft. He told the Associated Press that he stopped by the pool during a 103km (64-mile) bike ride on Friday just to see what was going on.

Hearn, a former Olympic canoe racer, said he reached into the pool because he wanted to examine the peeling new coating. He said he briefly touched a chunk that was still attached to the side of the pool, then let go shortly after a park worker told him to.

But, Hearn said, he was then detained by National Guard troops and Park Police for five hours before being released on Friday night.

“I’m a curious citizen,” Hearn told AP. “I reached down to see what it felt like. It was very rubbery.”

Trump, however, said on Friday, that the incident was “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”.

The US president was referring to the discovery of large numbers etched in discoloured grass on the National Mall the week before: “86 47“. Authorities said the numbers could have been meant as a threat to Trump, the 47th president. The number 86 can be slang for “getting rid of”.

Investigations into the matter are ongoing.

But experts have told US media that algae blooms in water are common at this time of year.

Rosalina Stancheva Christova, a professor of aquatic ecology at George Mason University in Virginia who took water samples from the pool for testing last Tuesday, told US radio broadcaster NPR on June 19 that the algae is “growing in excessive amounts” but is not toxic.

She said this kind of green algae is found all over the region during this time of the year and added that the reflecting pool provides  “excellent conditions” like strong sunlight and shallow and stagnant water, which promote its growth.

She added that “the disturbance of the pond during the renovations [is] accelerating this process [of the algae growth]”.

How much did this project cost?

A $14.7m contract to clean and paint the Lincoln Memorial Reflecting Pool was awarded by the federal government as a no-bid contract to Atlantic Industrial Coatings, based in New Canton, Virginia, on 3 April, according to the New York Times. Critics say it should have gone through a bidding process to ensure the best price.

Then, on June 16, the New York Times reported that a business called Greenwater Services of Brookfield, Ohio, linked to a longtime supporter of President Trump, was also given a no-bid contract to install a water-purification system in the Lincoln Memorial Reflecting Pool earlier in the spring. The company has now come under scrutiny because of the algae in the pool.

The report added that the company is owned by the JJ Cafaro Investment Trust, headed by John J Cafaro, a Trump donor who lives in Palm Beach, Florida near Mar-a-Lago, the president’s private club.

It is unclear why the contracts were awarded to these companies without a bidding process, but a White House spokeswoman told the New York Times last week that the president was not involved in selecting Greenwater Services.

Cafaro told Ohio newspaper The Vindicator that the contract for the work on the reflecting pool was awarded without a bidding process as “there is no one else in the world that does what we do”.

He added: “I’m nothing officially in the company [Greenwater Services]. They all work for me, but it has its own CEO and COO. I have so many different entities that I can’t keep track of them. That’s what the attorneys and the accountants are for.”

Which other vanity projects has Trump ordered, and who is paying for them?

Since the start of his second term as president, Trump has announced ambitious projects to renovate Washington DC monuments and the White House.

White House ballroom

Revamping the White House Ballroom is one such project. Last year, the president said he and wealthy donors would pay for the estimated $400m project, but then requested that Congress provide $1bn in taxpayer money for security upgrades to it. Senate Republicans, with an eye on the November midterm elections this year, said no.

The construction of the project, which began last year, has so far been funded by private donors, corporations and tech companies, including Google and Amazon.

Last October, Trump wrote on Truth Social: “For more than 150 years, every President has dreamt about having a Ballroom at the White House to accommodate people for grand parties, State Visits, etc. I am honored to be the first President to finally get this much-needed project underway – with zero cost to the American Taxpayer!”

Trump has also said, following its renovation, the building will have four-inch-thick windows and a drone protection base on the roof “to protect all of Washington”. It will also extend six storeys underground and include a military bunker.

The work to construct the ballroom, which will seat 1,000 guests, has faced significant public backlash. Preservationists and opponents assert that Trump exceeded his authority when he demolished the historic East Wing, which housed the offices of the first lady and the White House movie theatre, to make way for the new ballroom.

‘Arc de Trump’

Trump also plans to construct an “Independence Arch” across the Potomac River from the Lincoln Memorial and says he wants it to be bigger than Arc de Triomphe in Paris.

According to the spending plan released by the National Endowment for the Humanities in April, US taxpayers will fund the construction.

The height of the arch, with eagle statues and a Lady Liberty-type figure on top, has been estimated at 76 metres (250 feet) – to mark 250 years of American independence. That is higher than the Lincoln Memorial and not far off the size of the US Capitol, which at 88m (288 feet) can be seen across much of Washington.

By contrast, the Arc de Triomphe in Paris is 50m (164 feet) high.

Trump wrote in a social media post on June 4, “When completed, it will be, without question, the Greatest Arch of them all!”