Donald Trump’s $14.2m bid to turn the Lincoln Memorial reflecting pool from what the US president described as a “filthy” and “dirty” site into a “beautiful” monument has encountered a hitch.

The water is green again.

Days after the renovation was finished, algae has frustrated Trump’s attempt to transform the shade of the pool to “American flag blue” in time for the country’s 250th birthday.

The reflecting pool – one of Washington DC’s most historically symbolic attractions, and the scene of Martin Luther King’s 1963 “I have a dream” speech – has been one element of Trump’s efforts to recondition the country’s capital during his second presidency.

A no-bid contract to waterproof and repaint the site, which dates back over a century, raised eyebrows. It was awarded to a Virginia-based company, Atlantic Industrial Coatings, which had previously carried out work on a swimming pool at one of the president’s golf clubs.

The administration had claimed “residual” algae would be cleared in the immediate aftermath of the renovation. But it has proliferated amid warm weather.

The US Department of the Interior has claimed in recent days that the installation of a water treatment system which a spokesperson described as “nanobubbler technology” would help address the algae issue.

“The nanobubbler technology has successfully destroyed the algae bloom that has plagued every pool reopening since 1922,” a spokesperson told the Guardian on Tuesday. The spokesperson claimed the pool had been “broken and disgusting” days after a project that took place while Barack Obama was president.

“Now, due to deploying the advanced nanobubbler technology, the algae is dead and being vacuumed up as we speak,” the spokesperson added. “We thank President Trump for fixing the reflecting pool for good.”

In a 5 June post on his Truth Social platform, Trump claimed the renovation he ordered of the reflecting pool would stand the test of time. “This was not a paint job,” he said. “This was highly sophisticated material, industrial strength, that could last for 100 years, applied by very talented people.”

Administration officials have repeatedly claimed that other presidents tried and failed in years gone by to beautify the pool with “extremely costly” projects.

While Trump initially put the cost of this latest effort at about $1.8m, it quickly rose beyond $14m.

National Park Service employees were seen using skimmers on Monday in a bid to clean algae from the reflecting pool and return to it to the intended hue.