Algae grows in National Mall reflecting pool after renovation
Algae has appeared in the National Mall’s reflective pool, which underwent an expensive blue renovation ahead of America’s 250th anniversary, drawing mixed reactions from visitors.
The Lincoln Memorial’s reflecting pool is overflowing with algae, days after the landmark underwent a multimillion-dollar renovation, leaving visitors wondering if it will be ready in time for Independence Day, the 250th anniversary of America’s founding.
Photos taken over the weekend show National Park Service workers working to remove algae from a pool that has turned the water green. The basin in the pool was painted a deep navy “American flag blue” in preparation for Independence Day. The pool in Washington DC is approximately 2,000 feet long and 160 feet wide.
Renovation work began in April and was completed earlier this month. According to the New York Times, repairs to the pool cost a whopping $13.1 million.
In an earlier statement to USA TODAY, the Interior Department said the new color improves the pool’s reflective properties compared to the old gray concrete, which had become “slimy green” with algae buildup.
Environmental experts told USA TODAY the greenery could remain for months. Here’s what we know:
Expert: July temperatures could be bad news for reflecting pools
There are questions about whether the reflecting pool will return to its sparkling blue color ahead of the holiday season.
Hans Pearl, a research professor of marine and environmental sciences at the University of North Carolina at Chapel Hill, told USA TODAY on Monday, June 15, that the pool is still affected by algae and could appear green by the semi-quincentennial.
“Independence Day is probably the worst time of the year because the temperatures are the highest,” he said. “Mother Nature is really running the show.”
Algae thrives in hot climates, but disappears in winter, he explained.
DC is notorious for being hot and humid during the summer months. The National Oceanic and Atmospheric Administration told USA TODAY that this summer’s forecast is for above-normal conditions. In July, the region will experience several days of temperatures in the upper 80s to 90 degrees.
The region is also surrounded by many sources of moisture and moisture, including the Chesapeake Bay watershed and the Potomac River.
Pearl said pools need to be drained to remove algae. In that case, you will need to treat the water before refilling your pool. However, even after treatment, the water may still contain nutrients such as nitrogen and phosphorus that promote algae growth. Although these nutrients can be reduced, they cannot be removed to levels low enough to completely prevent algae from returning.
It is possible to treat water with chemicals such as chlorine, but the chemicals can affect animals such as ducks that drink pool water, Pearl said.
In addition, such treatment is expensive.
“The cure may be worse than the problem,” he said, and advised authorities to “wait and see” until cooler weather after September.
“You can understand colors a little bit more,” he added.
USA TODAY has reached out to the National Park Service and the Department of the Interior for comment. NPS previously announced it would collect and remove algae from pools.
Why was the reflecting pool renovated?
President Donald Trump announced plans to renovate the reflecting pool in April, according to a previous report by USA TODAY. He said the pool had been the subject of complaints due to leaking foundations and uncleanliness.
He told reporters that contractors will sandblast, caulk and resurface the pool basin. The pool is part of a citywide effort to spruce up landmarks ahead of Independence Day.
Before pool bottoms were made of concrete, pool basins were made of black asphalt. In some places, the water was dyed black to improve reflection. Before the renovation, the pool was leaking 16 million gallons of water a year, according to the National Park Service.
President Donald Trump selected Atlantic Industrial Coatings to perform the renovation work. President Trump said he chose the company because it worked at a golf club in Sterling, Virginia.
He continued to brag about the updated landmarks.
In a post on Truth Social on Monday, President Trump announced that his Fourth of July rally would be held on the National Mall “with the Lincoln Memorial in the backdrop and the beautiful new reflecting pool.”
What did NPS previously do regarding water?
The National Park Service typically takes several measures to prevent algae growth and maintain water quality in reflecting pools. A 2009 report said the agency was treating the water, removing debris and cleaning the pool.
The reflecting pool is filled with potable city water. The D.C. Water and Sewer Department treats water with chloramine, a disinfecting compound that lasts longer than chlorine and prevents contamination. This water has no long-lasting disinfectant effect once placed in the reflecting pool.
In addition, NPS treats the reflecting pool with a proprietary algae control agent. Still, algae growth has remained a consistent problem for many years. The report said authorities had previously considered various ways to combat algae growth. One method was to use a small device, about the size of a soda can, to emit acoustic frequencies that disrupted the bloom.
The Lincoln Memorial Reflecting Pool was constructed between 1920 and 1923.
Michelle Del Rey is a trending news reporter for USA TODAY. Please contact mdelrey@usatoday.com.
