President Donald Trump on Monday threatened jail time for anyone seeking to damage one of his signature renovation projects, the Lincoln Memorial Reflecting Pool in Washington, whose overhaul has become a political flashpoint.

Trump brought in contractors to drain the pool and repaint it "American flag blue." But soon after completion of the work, the coating has begun to peel off and algae turned the pool's water a mucky green — setbacks the president blamed on vandals.

"Of the MANY Statues and Fountains that we rebuilt, renovated, cleaned, and fixed, the only one that was Vandalized was the Reflecting Pool, which is being taken care of, ASAP!" Trump wrote on his Truth Social platform on Monday morning.

"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!" he added.

Law enforcement for the National Park Service told AFP, "Five individuals have been arrested for vandalism, and five additional individuals were issued federal citations."

From the algae blooms to peeling paint and green-tinted water, the reflecting pool has faced a string of setbacks since Trump ordered its renovation.

Trump, a real estate developer by profession, has blamed unspecified "sick, deranged" people for vandalizing the pool.

The president has launched a series of projects around Washington to put his stamp on the city, the main one being his expensive plan to build a huge ballroom at the White House.

The beautification drive has drawn criticism over the projects' cost, alleged lack of transparency in the awarding of contracts, and perceived extravagance at a time when many Americans are struggling with inflation.