Tests of the Reflecting Pool Turn Up a Surprise

The Reflecting Pool on the National Mall in Washington, D.C., is one of the most famous landmarks in the United States. But right now, it doesn't look like much of a landmark. Instead of shining blue water, the pool is filled with thick green algae — and workers have been scrambling to clean it up before July 4th celebrations. Scientists who tested the water say the cleanup effort has actually made things worse by helping a new, stubborn type of algae take over.

Workers tried to kill off the algae by pouring large amounts of hydrogen peroxide into the pool. That treatment worked on one type — a blue-green algae called cyanobacteria. This type of algae can sometimes produce toxins, which are harmful substances that can hurt people and pets. Scientists found very little of it left in the water. But the treatment didn't stop everything.

A new type of algae called Scenedesmus — a green algae that scientists have nicknamed 'Skinny Dead Mouse' — is now thriving in the pool. Scientists say this algae is a very aggressive grower, meaning it spreads quickly. 'What's happened is they've just switched the players,' said Hans W. Paerl, a professor at the University of North Carolina at Chapel Hill. 'And the green algae are just taking over.'

A reporter collected water samples from different parts of the pool and brought them to two scientists for testing. Some of the water samples were fairly clear, while others were dark green and thick. Greg Boyer, a professor at the State University of New York, ran tests and found the current algae are probably not toxic. 'They are stressed, but they are definitely not dead,' he said.

Both scientists say the methods workers are using — hydrogen peroxide and a technology called nanobubbles — are better at fighting blue-green algae. They don't work very well against the green algae that is growing now. Boyer explained that the Reflecting Pool is basically a perfect place for algae to grow. It is wide and shallow, which means sunlight reaches all the way to the bottom. It also has lots of nutrients in the water, and painting the bottom dark blue during a renovation made things worse by warming the water.

Workers have also been using giant vacuums to suck algae off the bottom of the pool. The job became so urgent that the National Park Service sent an email asking employees to volunteer for 12-hour shifts. The message called it a 'regional and national priority' and said it was part of 'critical pre-July 4th operational needs.' Some workers were even seen wearing waders — waterproof pants — and dress shirts, vacuuming algae right in the middle of the pool.

The federal government has not been very open about the water safety tests it has been running. A spokesperson said testing is happening but would not share the results. Scientists who asked for permits to do their own testing in the pool were not granted permission. That lack of openness is what led a reporter to collect her own water samples and bring them to independent scientists.

There is also a new problem with the pool itself. The sealant painted on the bottom as part of a $16.4 million renovation project is starting to peel off, and a large chunk was already missing last week. Tourists and local residents gathered around the pool, some hoping to grab a piece of the peeling sealant as a souvenir. One cyclist compared it to taking a piece of the Berlin Wall, saying, 'It's a piece of history.'

Scientists warn that the pool will likely stay green for a long time. As summer heats up, the blue-green algae could return by late July, which would bring back concerns about toxins. For now, the Reflecting Pool — a site where Martin Luther King Jr. once gave a historic speech — remains a murky, green mess.