Trump struggles to erase algae from Reflecting Pool

algae on – President Donald Trump’s plan to “beautify” Washington, DC by draining the Lincoln Memorial Reflecting Pool, coating it to look “American Flag blue,” and refilling it at a cost of more than $16 million has hit a fresh setback: algae spreading soon after the po

For weeks, the Lincoln Memorial Reflecting Pool was supposed to be a showcase—drained, lined, and reborn in a deep “American Flag blue” tied to the nation’s rapidly approaching 250th birthday.

It was a dramatic transformation: the 6.5-million gallon pool was drained. lined with a blue coating. and refilled. with a price tag of more than $16 million. But not long after the pool was filled earlier this month, the blue began to unravel. Algae started spreading in the water, turning the pool slime green. The blue liner began peeling off. Even after federal workers dumped jugs of hydrogen peroxide into the water, the algae bloom persisted.

The big question now is whether the pool can be cleared of algae by July 4. Several scientists said they’re skeptical that pond scum—technically described as plant-like algae—can be exterminated. And even if the water appears cleaner, they say algae returning may be only a matter of time.

At the center of the dispute is how fast microscopic algae can take over and what feeds it.

Algae—often described less affectionately as pond scum—gets its energy from sunlight. Some varieties are large, such as kelp or seaweed. Others are microscopic, comprising just a single cell. Those microscopic forms are the ones that bloomed in the Reflecting Pool. with reporting pointing to a common. non-toxic green algae variety known as Desmodesmus or Scenedesmus.

Jim Elser. an ecologist at the University of Montana who studies algae. said the pace is what makes these blooms so difficult to outpace. A single algae cell can divide two to three times per day, he said. That exponential growth is why a waterbody can shift from clear to murky in as little as 24 hours—if the conditions are right.

Those conditions, scientists say, are unusually well-aligned for the Reflecting Pool in summer. Green algae need sunlight. carbon dioxide. warmth. and. crucially. nutrients—especially phosphorus and nitrogen. the same elements used to fertilize crops. Elser’s basic point is simple: the pool in warmer months functions like a ready-made habitat for algae.

The Reflecting Pool’s physical setup makes it easier for sunlight to reach algae. The pool has an enormous surface area—roughly the size of six NFL football fields—and it is shallow. leaving a large volume of sun-drenched water. And in the outdoor heat—temperatures in the 80s and 90s—conditions for growth are accelerated.

Nutrients appear to be the real accelerant. The water used to refill the Reflecting Pool can be rich in phosphorus and nitrogen, and nutrients can also be added from the pool’s surroundings.

The water often comes from the Tidal Basin, a humanmade reservoir connected to the Potomac River. When that supply is too murky, government officials can fill the pool with DC Water, the city water supply. The Department of the Interior spokesperson said that’s what was done after the renovation.

But algae-friendly nutrients aren’t guaranteed to vanish just because the source is city water. Ashley Bair. a senior research developer at the water treatment company Usalco. said DC adds a form of phosphorus to its water supply to prevent lead and other heavy metals from leaching out of old pipes. She said that means even a pool fed by city water could still fuel an algal bloom if nutrients aren’t properly treated.

Then there is the pool’s immediate neighborhood. The Reflecting Pool sits in the middle of a city near parks frequented by geese and ducks. Ana “Mindy” Morales. an algae researcher at the University of Vermont. said droppings from wildlife can contribute nutrients that fuel the bloom. When it rains. Morales said. water can run off fertilized grass and pick up feces. spilling nutrients into the pool. which sits lower than the surrounding ground.

For all the effort to fight the visible green, multiple researchers said the root issue remains upstream.

The Reflecting Pool is equipped with a system that filters and treats water coming in, in part to curtail algae. But scientists said the system appears imperfect and not always on, and it does not appear to filter out the nutrients that fed this recent bloom.

The Trump administration has tried to kill the algae with hydrogen peroxide and a technology called nanobubbles, which can damage algal cells. Workers have also vacuumed the algae. But Elser said those efforts do not address the cause.

“They’re treating the symptom, not the cause,” Elser told me. “The cause is nutrients.”

If the goal is to keep the pool clear, Elser said, nutrients would need to be removed before they enter the pool—and workers would also need to keep removing nutrients after it’s filled. He pointed to one approach: using aluminum compounds that bind to phosphate and can then be filtered out.

Bair offered a different confidence. She said she’s sure she could have cleared up the algae. Her plan. as described. is to remove nitrogen and phosphorus as the water comes in. then kill the algae with chemicals such as hydrogen peroxide—similar to the administration’s approach—and clean them up. She also said regular monitoring of nutrient concentrations over time would be necessary. adding that it’s possible to do by July 4.

Other experts cautioned that chemical treatments can be temporary. Alan Wilson, an expert in algal blooms at Auburn University, said chemical treatments typically don’t solve the underlying conditions. He proposed a slower ecological option: adding organisms that eat algae, such as zooplankton. He described them as freshwater counterparts to “sea monkeys.”.

“If you can promote them, they’ll do their job,” Wilson said. He said that approach would take longer.

Wilson’s comments also came alongside a separate question about snails. Researchers said snails tend to target algae on the bottom and sides, so they would not fix a bloom where the algae is floating throughout the water.

Outside the technical debate, the pool’s appearance has begun to shift, though the story is still not over.

On June 23, my colleague Cameron Peters visited the Reflecting Pool and reported that the pool still had a green-ish hue, though the color appeared to be fading. Peters also saw a family of ducks standing by the pool’s edge.

Not everyone wants the water to look perfectly clean, either. Elser said his own view is more forgiving of nature’s mess.

“My feeling is that water with algae in it reflects the Washington Monument just as well with water without algae,” Elser said. “You will still get a reflection from a green pool.”

For now. the administration’s renovation gamble—turning a historic site into a blue spectacle for the 250th birthday—faces a stubborn biological adversary. The visible green may be fading, but the nutrient question remains. And that is the part most scientists say can’t be bulldozed with chemicals alone.

Lincoln Memorial Reflecting Pool algae pond scum hydrogen peroxide nanobubbles Desmodesmus Scenedesmus Tidal Basin DC Water phosphorus nitrogen Jim Elser Alan Wilson Ashley Bair Ana Mindy Morales July 4