Why the Reflecting Pool Is Full of Algae After Trump’s Renovation

On Wednesday morning, workers poured hydrogen peroxide into the Lincoln Memorial Reflecting Pool in Washington, DC.

The treatment is the latest attempt by the Interior Department to control an algae bloom that has turned the pool bright green, despite President Donald Trump’s costly renovation to make it “American flag blue” in time for the nation’s 250th anniversary. Hot temperatures and climate change are among the risk factors that could be driving the outbreak.

The Trump administration spent more than $14 million to update the pool ahead of celebrations across the US capital. The work was done under a no-bid contract by a company that has never worked for the federal government. (It has, however, worked on President Donald Trump’s golf courses, according to The New York Times.)

Algae began forming less than a day after the updated pool was unveiled last week. An Interior Department spokesperson told CNN that the bloom was due to “residual algae from the supply lines, which have been sitting dormant for eight weeks.”

One of the issues appears to be the water source. The Reflecting Pool usually draws water from the nearby Tidal Basin, which is often filled with algae. During periods with high amounts of algae, the water supply switches to municipal drinking water. The US Interior Department didn’t immediately respond to questions from WIRED about which water source is currently feeding the pool.

Another issue is the weather. High temperatures create “a perfect storm for [algae] to bloom,” says Hans Paerl, a former professor at the University of North Carolina’s Institute of Marine Sciences. Stagnant water, Pearl says, makes the problem even worse. “Lakes and reservoirs around the world—they all have this problem during this time of year.” Hotter-than-normal weather is expected to hit Washington, DC, to end the week, which could make controlling the bloom more challenging.

Paerl also points out another, related driver that the Trump administration has shown it’s not in a rush to resolve: climate change.

“It’s just getting hotter, and these blooms are expanding globally—they’re moving up into higher latitudes,” he says. “It’s clearly a temperature effect allowing them to optimize their growth.”

Beyond the hydrogen peroxide, the Interior Department is “deploying high-tech nanobubble ozone technology” to keep algae at bay, an agency spokesperson tells WIRED in an email.

Trump has touted the work on the pool, which includes painting it blue and fixing leaks, while also saying the company the government hired would be able to do repairs “in much less time, for much less money.”