Algae Coats $14.2 Million Lincoln Memorial Pool a Day After Refill

Q: After a $14 million upgrade, why did algae immediately plague the newly refilled reflecting pool?

The algae appeared immediately because the pool was in startup, not because the renovation had already failed. The Interior Department said the growth was “residual” algae left in supply lines that had sat dormant for about eight weeks during construction and was flushed into the pool when water service resumed. That explanation fits how large water features behave. Algae can quickly show up when stagnant water remains in pipes, sanitizer levels are still being stabilized, and the pool is suddenly exposed to sunlight and nutrients. Even with a new treatment system, startup periods often require flushing, balancing, and manual cleanup before water quality fully settles. The $14.2 million project was aimed at broader, long-running problems: leaks, aging surfaces, circulation and appearance. It included a new ozone nanobubbler filtration system intended to improve water quality and reduce future algae, but such systems do not instantly erase residue already in dormant lines on the first day of refill. Experts on large pools also note that renovation supports maintenance; it does not eliminate the need for ongoing treatment and cleaning. So the immediate algae was presented by officials as a temporary startup issue tied to dormant plumbing, while the real test of the upgrade was whether the new filtration and maintenance regime would keep the 6.75-million-gallon pool clear over time.

3 articles · Updated · CNN · Jun 10

Workers were clearing visible algae from the Lincoln Memorial Reflecting Pool on Wednesday, just one day after the newly renovated basin was refilled and publicly touted by the Trump administration.
The Interior Department called it residual algae from supply lines left dormant during eight weeks of construction and said a new ozone nanobubbler filtration system should keep the pool algae-free after startup.
The administration had promoted the project as proof Washington was looking "better than ever," while Trump repeatedly highlighted the renovation after long criticizing the pool as leaking and foul.
Costs also climbed sharply: Trump first suggested roughly $1.8 million, then $13.1 million, before the project settled at $14.2 million, still below a $35.3 million Obama-era contract estimate.
Visitors offered mixed reactions Wednesday, with some praising the pool's reflection and others questioning the blue-painted bottom and whether the spending was worthwhile.