The United States Park Police have arrested multiple people for allegedly vandalizing the Lincoln Memorial Reflecting Pool, President Trump said Saturday, days after algae turned the water a fluorescent green hue and rips appeared in an “American Flag Blue” surface handpicked by the president.

“The United States Park Police have arrested multiple individuals for vandalizing our Nations magnificent Reflecting Poll (sic),” Mr. Trump said in a Truth Social post Saturday. “Who would do such a thing? These are very serious crimes having to do with the destruction of National Monuments. Years in jail! Work will begin immediately on its repair.”

The National Park Service did not immediately respond to WTX US News’ request for comment.

David Hearn, a 67-year-old Bethesda, Maryland, man who stopped by the pool while on a 64-mile bike ride, said authorities arrested him and held him for five hours on Friday after he reached down into the pool.

Hearn, a former Olympic canoe racer who owned a company that provided materials to build watercraft, said it was scientific interest that drew him to the pool. He told The Associated Press he wanted to examine the peeling new coating on the bottom of the pool that Mr. Trump had ordered installed.

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.

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

In a Truth Social post Friday night, Mr. Trump alleged, without providing evidence, that three days prior, vandals had “destroyed the grass outside of the Pool” and had “also done everything possible to hurt the inside surface that was just installed.”

The Reflecting Pool has faced problems with leaks, algae and faulty plumbing for years. In April, the president launched an effort to address the pool’s “terrible” condition, part of a slate of spring cleaning projects in Washington, D.C., ahead of the nation’s 250th birthday.

After the pool was resurfaced and water was pumped back in, issues began to arise last week. Workers were seen in recent days removing algae from the Reflecting Pool, and on Tuesday morning, crews dumped bottles of hydrogen peroxide into the water.

Mr. Trump said Friday that “[t]he 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.”

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.

Mr. 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 on Truth Social.

That was a 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 Mr. Trump, the 47th president. The number 86 can be slang for “getting rid of.” They are investigating.