The Lincoln Memorial reflecting pool is set to be drained again after Donald Trump said on Monday – without providing proof – that five people were arrested for vandalism and five more are under investigation in connection to the algae blooms and peeling paint that appeared weeks after his ill-fated $14m renovation attempt.

“It’s not a lot of damage, but we’ll probably have to let the water out and refix it. They went in there with a knife,” Trump told reporters, describing what he first said was a 290- to 300ft slit in the paint but then later amended to a 350ft slit. He also said someone had put fertilizer into the water, which caused the algae to grow.

Reporters who visited the pool on Sunday could see no evidence of such damage, the Washington Post reported.

The newspaper also interviewed three-time Olympic cyclist David Hearn, who said he had been arrested by US park police on a misdemeanor charge after stopping by the refurbished pool and, out of curiosity, touching one of the pieces of peeling paint liner.

Trump has sought to turn the monument “American flag blue” in time for the for the country’s 250th birthday, which included painting the bottom of the pool a dark shade of navy officially called “Old Glory Blue”.

He awarded a no-bid contract to a company he said had previously done work on swimming pools at one of his golf clubs, and within days of the completion of the work, the water started to appear green from algae plaguing the standing water and the coating of paint applied during the renovation also started to detach.

On Monday, Trump was adamant it was not the pool company to blame for the algae blooms and peeling paint, but “vandals”. When pushed to provide evidence of his claims, he told reporters to call the Department of the Interior and the National Park Service. Neither agency responded immediately to a request for comment, nor did the US park police.

When asked how alleged vandals were able to get so close to one of Washington DC’s most historically symbolic attractions, where there is a heavy police presence, Trump responded that “we didn’t have a lot” of police then.

“Who would think that somebody would go into a pool and take a knife and start cutting it?” he asked.

It’s unclear when the pool will be drained, but a spokesperson with the DC Water Authority said the agency has issued the national parks service a temporary permit to discharge water into a sewer that flows into a local treatment facility. The permit was issued 16 June and expires 2 July, the spokesperson said.

Trump had earlier posted on social media that “there is a 10-year prison sentence for the destruction, or even the attempted destruction, of such things - Which will be fully enforced!”

Destruction of federal property ⁠can carry a maximum prison sentence of 10 years.