Trump claims arrests over vandalism at renovated Reflecting Pool

US President Donald Trump says federal authorities have made "multiple arrests" of people he said were vandalising the Reflecting Pool, as he struggles to explain why the multi-million-dollar renovation has seemingly backfired.

Mr Trump, who claims his predecessors had let the pool turn an algae-stained green, launched a $US14.2 million ($20.1m) project to turn the historic pool "American flag blue".

But after the new pool was unveiled, its blue tinge quickly became a familiar green. Workers treated it with chemicals to kill the algae, but then the painted blue lining on the bottom began to peel.

"We've had some real problems with Vandalism at the beautiful Reflecting Pool," Mr Trump posted on his social media site on Friday, local time.

"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."

The US president offered no details to substantiate his claim.

Agencies responsible for law enforcement and upkeep on the National Mall — the US Park Police, National Park Service and Interior Department — did not respond to AP's requests for comment.

Mr Trump on Saturday followed up by posting that Park Police "have arrested multiple individuals for vandalizing our Nations magnificent Reflecting Poll", later correcting his spelling to "Pool".

"Who would do such a thing? These are very serious crimes having to do with the destruction of National Monuments. Years in jail!"

One person arrested was David Hearn, a 67-year-old Maryland man who stopped by the pool while on a bike ride on Friday.

Mr Hearn, a former Olympic canoe racer, said he was a "curious citizen" and wanted to examine the peeling new coating on the bottom of the pool.

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, before he was detained by National Guard troops and Park Police for five hours before being released.

"I'm a curious citizen," Hearn said in a telephone interview.

"I reached down to see what it felt like. It was very rubbery."

The Washington Post first reported on the arrest of Mr Hearn, who said he had a date to appear in court next month and was looking for legal help.

The pool is marred by clouds of algae in the green water, with swaths of loose blue paint detaching from the bottom.

Mr Trump insisted something nefarious had been going on at the scene.

"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," he posted on Truth Social.

That was an apparent reference to the discovery of large numbers "86" and "47" etched in discoloured grass on the National Mall the week before.

Authorities investigating the matter said the numbers could have been meant as a threat to Mr Trump, the 47th president. The number 86 can be slang for "getting rid of".

Mr Trump's claims came after days of negative attention to the state of the pool, which he is redeveloping ahead of the coming America 250 celebrations.