Trump said his predecessors had let the pool turn an algae-stained green and that he’d line it with “American flag blue” so it better reflected the Washington Monument. 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.

On Friday night, Trump posted about the pool.

“We’ve had some real problems with Vandalism at the beautiful Reflecting Pool,” he posted on his social media site Friday night. “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.”

He offered no details to substantiate his claim.

Agencies responsible for law enforcement and upkeep on the National Mall — the U.S. Park Police, National Park Service and Interior Department — did not respond to requests for comment. Trump on Saturday followed up by posting that 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 owned a company that made composite used to build watercraft. He said he stopped by the pool during his 64-mile bike ride Friday to see what was going on.

Hearn, a former Olympic canoe racer, told The Associated Press that 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 Friday night.

“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 Hearn’s arrest, and he said he has a date to appear in court next month and is looking for legal help.

Even if someone pulled ribbons of paint from the side of the pool, it would not explain the clouds of algae in green water and swaths of loose blue paint detached from the bottom.

Trump insisted something nefarious has 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 Friday evening.

That was an apparent reference to the discovery of large numbers etched in discolored 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.” They are investigating.

Trump’s claims came after days of negative attention to the state of the pool, which has drawn television cameras and curious onlookers.