A liner along the bottom of the Lincoln Memorial Reflecting Pool was cut with a sharp knife or razor this month, causing damage to the foam sealant installed as part of a multimillion dollar rehabilitation project, the US National Park Service says.

The agency reported the June 9 incident to US Park Police, deputy director of operations for the park service Frank Lands said.

Lands made the statement in a court document filed late on Wednesday as part of a lawsuit filed by a nonprofit organisation to halt work on the $US16 million ($A23 million) rehabilitation project by US President Donald Trump's administration.

The police report indicates damage to the pool, "including a caulk over the foam sealant that was cut with a sharp knife or razor and destruction of delaminating surface material," Lands said.

About 70 fence post tops also were thrown into the pool, he said.

The statements mark the first time the administration has offered specifics for when and how the Reflecting Pool may have been damaged after work on the project was substantially completed.

Trump and other officials have blamed unidentified vandals for peeling paint as well as a "350-foot gash" in the liner and other problems.

Six people have been arrested, Trump said this week, without providing details.

Trump pledged to beautify the century-old Reflecting Pool before the United States' 250th birthday celebrations, draining its water and directing the bottom to be painted a colour he called "American flag blue".

But since the site was restored, its water has been plagued by an algae bloom and pieces of the new coating have appeared to be peeling off the bottom.

His administration faces a self-imposed deadline to complete the renovation before July 4.

Trump said on Wednesday that "sick people" had used razors and box cutters to slice portions of the lining.

The US Park Police posted surveillance footage on Wednesday evening and asked for help "identifying the individual depicted here in connection with a Destruction of Government Property investigation".

The grainy, 30-second video appears to show a person kneeling down, reaching into the reflecting pool and removing something from the water.

Police said it was taken on Friday afternoon.

In his statement to the court, Lands said the parks agency plans to begin draining the Reflecting Pool following Independence Day celebrations to conduct repairs, including assessing and repairing any damage to the lining.