How the National Mall's Other Reflecting Pool Stays Clear of Green Algae

Two large reflecting pools sit less than two miles apart on the National Mall in Washington, D.C. One of them — the Lincoln Memorial Reflecting Pool — has been covered in green algae and linked to the deaths of several ducks. The other, the Capitol Reflecting Pool near Capitol Hill, looks clean and clear. So why is one pool doing so much better than the other?

The two pools are run by different groups. The Lincoln Memorial pool is managed by the National Park Service. The Capitol pool is overseen by a government official called the Architect of the Capitol. That difference in management plays a big role in how each pool is maintained.

The Capitol pool is smaller and shaped like a trapezoid, which is a four-sided figure with two parallel sides. Because it is smaller, workers can drain it, clean it, and fix up its concrete basin in just one week every fall. Sometimes they also clean it in the spring. The Lincoln Memorial pool, on the other hand, is long and narrow. Draining and refilling it takes about a month.

Thomas Austin, the Architect of the Capitol, spoke to the news outlet Politico about the challenges of keeping any large pool clean. He said it is hard to compare the two pools fairly because they were built differently and at different times. The Lincoln Memorial pool was finished in 1922, while the Capitol pool was completed in 1971. "I will not say that our full reflecting pool is without problems, because it certainly does have some issues," Austin said.

Austin also explained that all large water features are tough to maintain over time. Pumps, pipes, animals, bacteria, and algae are just some of the problems that come with them. "They require pumps, require pipes — corrosion, animals, diseases, bacteria, algae. There's a lot of things that go along with that," he said.

The Lincoln Memorial pool has faced serious problems since a recent renovation. Workers painted the floor of the pool with a blue rubber coating and used a strong form of hydrogen peroxide to kill an algae bloom. Earlier this week, people nearby reported seeing three dead ducks in the water. The White House defended the project, with spokesperson Taylor Rogers saying that by Thursday the pool was "crystal clear and is reflecting perfectly."

The Capitol pool was once managed by the National Park Service, too. In 2011, Congress transferred control of it to the Architect of the Capitol. At that point, the Park Service had planned to build a shallower pool with a drain that could empty it overnight. Instead, the Architect completed a $7.3 million repair and cleaning project on the existing pool. Workers even added special ramps to help baby ducks get in and out of the water safely, though some members of Congress criticized that expense.

The Capitol pool has had its own problems in the past. In 2008, a disease called avian botulism killed at least two dozen ducks there. In 2020, high temperatures caused an algae bloom. So while the Capitol pool is doing better right now, it is not perfect either.

Lawmakers who help oversee the Capitol grounds have shared different views on the situation. Democratic Senator Chris Van Hollen of Maryland praised the Capitol pool's upkeep. Republican Representative Stephanie Bice of Oklahoma simply said "size matters." Democratic Senator Martin Heinrich pointed to the timing of the White House's renovation project as the main problem, saying that anyone who took an eighth-grade science class could have predicted things would go wrong.