Green algae has again taken over the Lincoln Memorial Reflecting Pool, just days after the landmark reopened following a multi-million-dollar renovation.

US President Donald Trump spent $14 million to seal the concrete bottom with an "American flag blue", but the pool has turned a murky green, forcing a monumental clean.

The National Park Service initially indicated the return of the green-looking water was due to dormant algae that sat in the pipes for weeks and returned when the pool was being refilled.

"It's part of the normal startup process," a spokesperson for the agency told CNN.

"We are removing the algae, and the nanobubblers will maintain the pool and keep it algae-free."

The algae appeared to have remained just as entrenched over the weekend despite the cleanup efforts.

A spokesperson for the Department of the Interior told The Post that the algae of previous administrations has been killed by technology implement by the Trump administration and is now being removed.

"Versus previous administrations, the National Park Service is actually maintaining the beautifully completed Reflecting Pool," the spokesperson said.

"The nanobubbler technology has successfully destroyed the algae bloom that has plagued every pool reopening since 1922, most infamously, the Obama pool reopening that resulted in massive algae clumps taking over the pool's surface.

"Now, due to deploying the advanced nanobubbler technology, the algae is dead and being vacuumed up as we speak. We thank President Trump for fixing the Reflecting Pool for good."

The Trump administration spent an addition $1.7 million on an upgraded ozone nanobubbler filtration system, which is intended to disperse tiny oxygen bubbles to undercut algae's food supply.

The 6.7-million-gallon pool, first constructed in the early 1920s, has faced a recurrent algae issue.

The Obama administration spent $34 million fixing the Reflecting Pool's piping and filtration system to circulate water from the Tidal Basin. That renovation was intended to fix its persistent algae and leak problem, but both issues returned.

Trump has often commented on the "disgusting," "filthy," and "dirty" conditions of the pool under his predecessors.

He previously said that his planned beautification project would only cost $1.5 million to $2 million. He also said he rejected a proposal for a $300 million overhaul to replace the pool's bottom with stone.

Instead, Trump chose to reseal the gaps and add an "American flag" blue-tinted coating on the bottom.

A goal of the project was to stop the leaking in the pool, which experts have said is due to gaps between the expansion joints and its piping system.

Prior to Trump’s latest renovations, the Reflecting Pool leaked some 16 million gallons of water every year, according to the Department of the Interior.

Some have argued that the leaky pipes that help push out four million gallons of water roughly every three days are also to blame for the algae, in addition to the leaks, because they undermine the filtration system.

The Trump administration is planning to repair those pipes in the fall, according to the Interior Department.