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Algae clouded Trump’s vision for the Reflecting Pool. But scientists aren’t surprised
Algae turns the newly repainted Lincoln Memorial Reflecting Pool green on the National Mall on Tuesday in Washington, DC.
Chip Somodevilla/Getty Images
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Chip Somodevilla/Getty Images
WASHINGTON — The Lincoln Memorial reflecting pool is once again making headlines, this week for turning green.
The Washington, D.C. landmark was refilled with water earlier this month after President Trump had its neutral grey bottom repainted “American flag blue.” The multi-million dollar project produced subtle results in the eyes of many observers, even as Trump and Secretary of the Interior Doug Burgum — whose agency managed the renovation — touted its success.
In recent days, however, the pool has taken on a verdant hue — the result of algae blooms that experts say are to be expected in these conditions.
“It’s called ‘New Pond Syndrome,’” says Steve Goodale, a Canadian swimming pool specialist known online as “Swimming Pool Steve.” “It’s a known thing that happens when you take a natural, clear body of water like this that sits in an open air environment and you try to start it up, very often you end up with green water almost immediately.”
Goodale says the process took longer — a matter of days — to unfold in this case likely due to the sheer size of the pool, which measures 2,030 feet long and has a surface area of approximately 338,000 square feet.
“Excellent conditions” for algae growth
Rosalina Stancheva Christova, a professor of aquatic ecology at George Mason University in Virginia, took water samples from the pool on Tuesday. She confirmed the algae belongs to the genus Desmodesmus, which she said is “growing in excessive amounts” but is not toxic or harmful.
Christova says this kind of common green algae is found all over the region, especially this time of year. The reflecting pool in particular provides “excellent conditions” for algae growth, she said: shallow, stagnant water, strong sunlight and no shade.
“It could happen every single summer,” she added. “But it seems that the disturbance of the pond during the renovations [is] accelerating this process.”

Christova said last month’s renovations may have affected the balance of nutrients in the pool, potentially accelerating the algae blooms. Goodale similarly views the resurfacing as one of several contributing factors.
“The new, darker interior surface is going to absorb more sunlight,” Goodale says. “It is going to result in water that’s warmer, and that ultimately is going to lead to more prolific algae growth.”
A microscopic slide shows the Desmodesmus algae that quickly turned the Reflecting Pool’s water green. The new dark blue paint of the pool’s lining makes the water warmer and friendlier to the algae growth.
Rosalina Stancheva Christova, PhD.
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Rosalina Stancheva Christova, PhD.
The Trump administration has said the algae came from residual material in supply lines that had lain dormant for weeks. Their growth was likely exacerbated by the extreme temperatures that hit D.C. last week, bringing heat index values to 95 degrees and above.
Algae has resurfaced in the reflecting pool periodically over the years — including immediately after it reopened from its last major renovation in 2012, forcing the National Park Service to drain it, refill it and recalibrate its ozone level. And in 2019, crews had to drain four million gallons from the pool to fix a broken water line that had algae growing in it.
An Interior Department spokesperson told NPR over email that algae and other contaminants have “long plagued the Reflecting Pool since 1922,” pointing to the Obama-era renovation as an example.
“Unlike under Obama and Biden, the National Park Service is actually maintaining the beautifully completed Reflecting Pool,” they added.
Responding with tiny bubbles and big vacuums
Workers battle the fast-growing common algae in the Lincoln Memorial Reflecting Pool on Thursday.
Rachel Treisman/NPR
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Rachel Treisman/NPR
The Trump administration is using a mix of mitigation strategies, including pouring hydrogen peroxide into the water to kill the algae.
The Interior Department says hydrogen peroxide is a “milder treatment than chlorine and is used in spas and specialty pools like natural swimming pools,” adding “there are no harmful side effects to marine life or to the environment.”
Workers are also deploying what the department calls “high-tech nanobubble ozone technology” to neutralize algae and other pathogens in the pool. The department says that approach is validated by several universities and the National Oceanic & Atmospheric Administration.
Those ozone bubbles are so tiny the human eye can’t even see them, Goodale says.
“The best way to describe it is that the bubbles are neutrally buoyant, so they won’t just rise to the surface and disappear readily,” he explains. “They can last for weeks, if not months in the water, doing their oxidizing thing and keeping the algae at bay.”
‘A monumental effort’
Goodale says it’s more complicated than treating the average backyard swimming pool, since the reflecting pool — despite its name — is actually more akin to a “manmade shallow lake.” He says it’s hard to predict just how long it will take to completely solve the algae problem, calling it “a monumental effort, literally.”
The Interior Department posted on X Wednesday that the nanobubble technology had “very effectively killed the algae,” and National Park Service crews would spend several days vacuuming up the dead algae from the bottom of the pool.
But as of Thursday morning, much of the pool — especially in the center — was still bright green.
Work continued on both ends of the pool. Nanobubble machines deposited their tubes into the water, as mobile vacuuming systems known as “trash pumps” hummed loudly from the shore. Handfuls of workers stood either in the pool or on the edge maneuvering long-handled vacuums back and forth. Their contents, including pistachio-colored water, poured out of hoses laying in the nearby grass.
The work zones were marked off by orange cones, but passersby walking the length of the pool appeared relatively unfazed. Some stopped to peer down and snap pictures of the water itself — including sections of paint that had visibly peeled off — while others were more focused on getting a photo of the Washington Monument in the background.
Loay Hidmi was walking deliberately along the edge of the pool closest to the Lincoln Memorial, hands clasped behind his back, looking over the ledge. The relatively new D.C. resident is a civil engineer who specializes in water treatment, and has been coming by the pool all week to see the progress for himself. He estimates it’s about 80% of the way there.
“I’m taking pictures of it … for the last week and I can see the gradual change,” he said. “So I’m hopeful. But we’ll have to see if it gets sustained.”
What happens next?
Hidmi worries that the algae could come back, given the favorable conditions posed by the sunny, shallow pool.
He acknowledges that’s mostly an aesthetic concern, given how much the administration has just spent on repainting the pool, but says it also raises questions about their process.
“In water systems, when you fix something, you need to look at the step before it and the step after,” he said.
Goodale agrees. He says that when a water system is taken offline, the pipes still remain full of water — “they don’t just gravity-drain away” — and need to be flushed out before any refilling. And he says eliminating algae is no substitute for dealing with underlying filtration issues.
“That’s like the equivalent of mowing the lawn when perhaps it needs to be something else that addresses the source nitrates and phosphorus, so that it’s more like pulling the weeds out by the root,” he says.
The algae doesn’t bother the ducklings swimming in the Reflecting Pool. Experts say the hydrogen peroxide used to get rid of the algae is safe for them, too.
Rachel Treisman/NPR
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Rachel Treisman/NPR
In the meantime, Christova, the algae expert, would like to see the water monitored weekly.
“If we don’t have any control over algal growth, we don’t know what is growing,” she said, adding that not all types of algae are as harmless as the one currently blooming in the pool.
When asked about plans for maintenance and algae prevention, White House spokesperson Taylor Rogers told NPR: “Thanks to President Trump, new lining and industrial grade materials will permanently seal the Reflecting Pool, which previously leaked 16 million gallons per year and wasted countless taxpayer dollars.”
Even after the Obama-era renovation, the reflecting pool suffered from broken pipes and water leaks requiring costly refills, according to a Department of the Interior report from fiscal year 2023. It called for new expansion joints, supply and return lines with thicker walls, saying “an improved distribution system will ensure the water can be circulated through the treatment plant, filtered, and treated with ozone.”
This latest renovation does not appear to have addressed the pipe problems, even though it did involve replacing failing expansion joints, resealing the pool, removing truckloads of garbage and “fixing the water system, drainage and so much more,” as Trump wrote on Truth Social in May.
Along the way, the cost of the project grew from Trump’s initial $2 million price tag to at least $14 million. Federal contract records show the government is paying $1.7 million to an Ohio-based company for the nanobubble technology alone.
“The scope of the Project has been greatly enlarged as we became involved because we realized how important it would be to Washington, D.C., and the record number of visitors coming to our now very safe Capital for all of the upcoming events in celebration of our 250th Anniversary,” Trump wrote.

The National Mall is hosting a number of semiquincentennial events on and around July 4, including a weekslong state fair that kicks off Wednesday evening.
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Trump’s ‘American Flag Blue’ in the Lincoln Memorial pool is already gray — and the Olympic canoer ‘vandal’ is fighting his arrest | Fortune
The newly drained Lincoln Memorial Reflecting Pool’s bottom surface has noticeably faded since it was lined with a protective coating in a color President Donald Trump called “American flag blue” this spring.
An Associated Press reporter and photographer viewed the fenced-off Reflecting Pool on Wednesday from the top of the Washington Monument. The new liner appears grayer than when the pool was repainted and refilled with water in early June. Debris that had been visible earlier this week after the pool was drained is now largely gone, after work crews removed it.
Trump’s problem-plagued effort to revamp the landmark has stretched well past his initial goal of having the Reflecting Pool ready by July 4 for the nation’s 250th birthday.
The president at first suggested his renovations would cost $1.5 million, but the bill ballooned to more than $16 million by June.
Trump had said the repairs would last a century, but within days of the project’s initial completion last month, the water was beset by an algae bloom and pieces of the new coating appeared to be peeling off the bottom.
Ohio-based Green Water Solutions, also known as Greenwater Services, was given a $1.7 million contract to install a water-purification system in the Reflecting Pool, while Virginia-based Atlantic Industrial Coatings was awarded $14.7 million to repaint and waterproof the pool’s concrete floor.
Vandalism charges were levied against a former Olympic canoeist
Trump has repeatedly blamed vandals for the peeling paint, though critics allege it’s from shoddy repair work.
Trump has said, without citing evidence, that vandals made a “350-foot gash” in the liner and caused other problems. No large slash marks were immediately visible Wednesday from the Washington Monument view. It was not possible to do a more up-close inspection of the entire pool due to a dark fence surrounding the perimeter.
Interior Secretary Doug Burgum, whose agency oversees the National Park Service, said that after the water is drained and debris is cleaned from Independence Day fireworks, the plan for the pool is straightforward: “Repair the vandalism that was done. Fill it back up again.” He was speaking with conservative podcaster Katie Miller.
Court documents show that the National Park Service reported to the U.S. Park Police a June 9 incident in which a sharp knife or razor was said to have cut the pool’s new liner.
Former Olympic canoe racer David Hearn pleaded not guilty last week in D.C. Superior Court to deliberately damaging the Reflecting Pool. Hearn has said he reached inside the pool to examine the peeled sealant and let go of a chunk when he was told to by a park worker.
His attorneys and other Trump administration critics have derided the case as an abuse of prosecutorial power and maintain he is being scapegoated for the poor job done fixing up the Reflecting Pool.
At least three other people have been charged in the same court with misdemeanors for allegedly removing pieces of paint from the pool, court records show. All three pleaded not guilty during initial court appearances.
The work on the Reflecting Pool is just one of a number of projects Trump has spearheaded across the nation’s capital. Most prominently, he demolished the White House’s East Wing to build a $400 million ballroom and plans to build a towering arch. between the Lincoln Memorial and Arlington National Cemetery.
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Argentina is back in the World Cup final after a thrilling semifinal win over England
Argentina’s Lionel Messi celebrates the team’s second goal by Lautaro Martínez during their World Cup semifinal against England on Wednesday in Atlanta. Argentina defeated the English 2-1 to advance to Sunday’s final against Spain.
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Shaun Botterill/Getty Images
ATLANTA — Argentina, the death-defying defending World Cup champion, will play for a second consecutive title after scoring two late goals to beat England in the semifinal, 2-1.

For a fourth straight knockout game, Argentina survived a heart-stoppingly close call. First was Cape Verde, the African island nation underdog, who took the champions to extra time. Then was the furious miracle comeback after Egypt took a 2-0 lead. Then, in the quarterfinal, a shorthanded Switzerland squad forced extra time despite a 72nd-minute red card.
This gutsy Argentina squad prevailed in all three games, and Wednesday, they pulled it off yet again. In the 55th minute, England took a 1-0 lead when forward Anthony Gordon tapped in a cross.
But, as the clock ticked up, Argentina turned up the intensity. A relentless onslaught yielded near miss after near miss before finally midfielder Enzo Fernández scored off a rocket from outside the penalty area to equalize the game at 1-1 in the 85th minute.
Then, in stoppage time, forward Lautaro Martínez sent the Argentina crowd into delirium with a header off a cross from 39-year-old superstar Lionel Messi, who assisted on both goals.
“I think that this team plays the best when we are facing a difficult situation, with adversity, ” said Argentina coach Lionel Scaloni afterward. “We had a challenging game, a challenging situation. There was blood in the water, and we went for it.”
In Sunday’s final they will face Spain, which defeated France on Tuesday 2-0 to contend for their second-ever title.
England’s Anthony Gordon celebrates scoring his team’s first goal during the World Cup semifinal against Argentina on Wednesday in Atlanta.
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Justin Setterfield/Getty Images
Wednesday’s game, the sixth meeting between these two teams at the men’s World Cup, was the newest chapter in their storied rivalry. That history includes the infamous “Hand of God” goal scored by Diego Maradona in the 1986 World Cup, four years after a war between the two countries over the Falkland Islands. The British won the war, but the sovereignty of the territory is still under dispute.
(Asked Tuesday about the “Hand of God,” which was the first of two goals scored by Maradona, coach Scaloni slyly deflected. “I think all of the world remembers that game, remembers Diego’s performance, remembers above all the second goal,” he said.)
To hear England’s coach, none of that mattered on Wednesday. “We respect our opponent, but we don’t dip in historic events, and we don’t make it bigger than it is,” Thomas Tuchel told reporters the day before the match.
Yet from the opening kick, both teams eagerly played a physical game: Collisions, jersey tugs, tough tackles, bodies flying to the ground. Referee Ismail Elfath, the first American man to work a World Cup semifinal, awarded a yellow card to each team before halftime.

And after the game, as Argentina’s players celebrated on the field, midfielder Giovani Lo Celso, who did not play in the match, unfurled a white banner bearing the words “Las Malvinas son Argentinas,” or “the Malvinas are Argentine,” a reference to the Argentine name for the Falkland Islands. The banner appeared to have been first held by Argentina fans in the stands.
For England fans, the pain is a familiar one as they watched the team fall short in yet another major tournament knockout game. England lost in the Euros final in both 2024 and 2020, and the last time they reached the World Cup semifinal in 2018, they lost by the same score as Wednesday’s match, 2-1, despite scoring first.
England’s forward Harry Kane (#9) and teammates react after losing their World Cup semifinal match 2-1 against Argentina.
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Odd Andersen/AFP via Getty Images
“It’s a similar story to what’s happened in previous tournaments,” England Captain Harry Kane conceded afterward. “We’d done so well for that 60 minutes. We scored. We deserved to be ahead. And then, for one reason or another, we struggled to keep the ball. We struggled to put pressure on the ball and it just allowed them to create more momentum.”
The atmosphere inside Mercedes-Benz Stadium in Atlanta was raucous and ear-splitting. Argentine fans by the thousands wore the white and sky blue striped jerseys bearing the name of their star Messi. The English celebrated their team wearing all-white or all-red jerseys of their scoring sensations: Kane and Jude Bellingham.
But neither star could save England from another defeat, extending what has already been an agonizing 60-year wait to return to the final.
NPR’s Russell Lewis contributed reporting from Atlanta
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ICE should do traffic stops despite recent shootings, Trump says, seeming to oppose new suspension
WASHINGTON (AP) — The Immigration and Customs Enforcement agency should continue vehicle stops after recent fatal shootings, President Donald Trump said on Wednesday, seeming to oppose a new suspension of the practice used as part of his immigration crackdown.
ICE is “doing a GREAT job, one that has to be done,” Trump wrote on his social media site.
The Republican president said that to remove criminals he claims were let into the country under the previous Democratic administration “we must be strong, tough, and smart, and we CANNOT give up one of ICE’s most important and effective Crime Fighting tools, THE TRAFFIC STOP!” Trump said, “Once we do, we are playing right into the criminal’s hands.”
Trump administration officials have told Immigration and Customs Enforcement officers to suspend most vehicle stops after two deadly shootings within a week, people familiar with the decision said Tuesday.
The suspension was ordered after an ICE officer shot and killed a Colombian driver Monday in Maine and a week after another officer shot and killed a motorist in Houston, renewing criticism of the agency’s enforcement tactics that were widely condemned last winter after the killings of Alex Pretti and Renee Good in Minnesota.
In Florida on Tuesday, a third man in roughly a week died during an encounter with immigration officers. This time, a 28-year-old man was killed after he was hit by a tractor trailer while running from immigration and other federal officers, authorities said.
It’s a narrative that has been repeated again and again since the Trump administration’s immigration crackdown began, with federal officers confronting drivers and then saying they opened fire when the drivers’ vehicles became a danger. That’s despite decades of warnings from policing experts that shooting into moving cars presents a danger of its own and should almost always be avoided.
There have been at least 10 deaths involving encounters with immigration agents since Trump launched his deportation campaign. At least four of those deaths involved people in vehicles, including the one last week in Houston, a trend so troubling that U.S. Sen. Susan Collins, R-Maine, said Tuesday that she had urged Department of Homeland Security Secretary Markwayne Mullin “to cease all non-urgent vehicle stops.”
John Sandweg, who was acting director at ICE, which is part of DHS, during President Barack Obama’s Democratic administration, estimated recently that there have been roughly 18 traffic stop shootings during the Trump immigration crackdown.
The office of Maine Sen. Angus King, an independent who caucuses with Democrats, was told by DHS that ICE was suspending traffic stops, office spokesperson Matthew Felling said.
ICE, which has been under pressure to beef up arrest and deportation numbers, often says people it’s trying to arrest are increasingly resistant to leaving their homes. ICE officers blame immigration advocates who advise immigrants to stay in their homes unless ICE produces a warrant signed by an independent judge instead of the administrative warrants the agency generally uses that are signed by another ICE officer. So, ICE officers say, they’re forced to find other areas in which to make arrests.
Shooting angers Maine
Hundreds of people in Maine protested Tuesday over the fatal shooting of Johan Sebastián Durán Guerrero, a 25-year-old Colombian national. Advocacy groups said Guerrero, who had a wife and a young daughter, was authorized to work in the United States.
DHS said Monday that an officer, “fearing for public safety,” shot and killed Durán Guerrero while officers were watching the home of someone they believed was in the U.S. illegally and facing a final order of removal from the country. It said in a post on X that when ICE tried to stop a car driven by someone who came from the home, the person attempted to flee in the vehicle and the officer fired.
That was a shift from how King earlier described the encounter, when he said Mullin told him the officer opened fire after the man tried to use his vehicle as a weapon. King said Mullin told him the officers were trying to serve an arrest warrant but not for the man who was shot.
In a scathing post on X, outgoing Colombian President Gustavo Petro called the shooting a targeted killing “at the hands of the U.S. government.”
Petro, who has openly quarreled with Trump, urged Trump to provide an explanation and accused ICE officers of treating Durán Guerrero as “an inferior being without rights.”
In Wednesday’s social media post, Trump told ICE to be “judicious, fair and smart, and go back and do your very important job.”
Maine’s congressional delegation on Tuesday demanded a “comprehensive, transparent, and expedited investigation.”
Questions surround the shooting
Photos showed bullet holes in Durán Guerrero’s car windshield, but the officers involved in the shooting didn’t have body cameras, leaving many questions. Among them are how close the officer was to the vehicle when shooting, whether officers told Durán Guerrero to stop and why ICE believes he had put the public in danger.
Border czar Tom Homan told reporters Tuesday that the investigation needs to play out and that officers will be held accountable if they are found to have acted inappropriately or illegally.
Maine’s attorney general’s office, which said it is working with federal agencies to investigate, said initial statements suggest the driver was trying to flee in the direction of the officer, whose name hasn’t been released and who was placed on leave.
Collins said Mullin told her the DHS inspector general is investigating in cooperation with the FBI.
Democrats seeking to unseat Collins in November have sought to connect her with ICE’s methods, which have drawn public scrutiny and derision. Collins later said in a statement that although ICE needs to improve, eliminating the agency would make the nation less safe.
Maine Secretary of State Shenna Bellows, a Democrat who is vying for Collins’ seat, called the ICE officers at the shooting “thugs” during a vigil Tuesday in Lewiston.
___
Whittle contributed from Biddeford, Maine; Brook from New Orleans; and Sisak from New York.
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