At least five people have been arrested for allegedly vandalizing the Lincoln Memorial Reflecting Pool, an administration official said Monday, as President Donald Trump threatened long prison terms for offenders.

The five arrests and five additional citations to other alleged offenders have come in the wake of Trump saying on Saturday, with no evidence so far, that vandals at the Reflecting Pool cut a 250-foot-long “gash into the beautiful facade of what took so much work, competence, and money to build and complete.”

Among those arrested was former U.S. Olympic canoeist David “Davey” Hearn, who previously told NBC News he was detained for five hours Friday after touching a piece of detached coating at the Reflecting Pool.

Over the weekend, following a meeting with contractors at Camp David, Trump said the Reflecting Pool would likely need to be drained again.

Marine One was spotted on Sunday flying over the area, and Trump said he’d “inspected” the Reflecting Pool.

Trump on Monday morning repeated his claims that the Reflecting Pool is under attack ahead of the nation’s 250th birthday in two weeks. In a post on Truth Social, the president said that the Reflecting Pool has “been given a 300-foot-long gash” as “chemicals have been illegally” placed in the water.

“Please remember that there is a 10-year prison sentence for the destruction, or even the attempted destruction, of such things — Which will be fully enforced!” Trump added in his Truth Social post.

There were no social media postings or other immediate evidence to show that grass near the Reflecting Pool had been damaged with an “8647” message.

The term “86” is often used to mean throwing out or removing an item. That term, when added to the number 47, has been interpreted as a threat against Trump, the nation’s 47th president, according to federal prosecutors.