Algae persist in in the Reflecting Pool, despite the Trump administration’s efforts to clear murky waters.
Just days after the Trump administration completed a multimillion-dollar renovation to turn the Lincoln Memorial Reflecting Pool American flag blue, residents and online users noticed that the pool had turned phosphorescent green.
Here’s why:
The calm, still waters of the Reflecting Pool make it an ideal breeding ground for algae growth. Algae needs nitrogen and phosphorus to grow, and the Reflecting Pool is fed primarily by the Potomac River, which receives high doses of these nutrients from nearby urban and farmland.
The Potomac also absorbed one of the largest sewer spills in U.S. history earlier this year, when a pipe burst three miles upstream from Washington; however, this event probably occurred too long ago to have contributed to today’s algal bloom.
Untreated sewage is high in nitrogen and phosphorus. When nutrient levels are high, feasting algae can proliferate rapidly.
The Ministry of Internal Affairs said when the algae first appeared “Now,” From the supply lines to the pool.
Experts also think that the dark blue color may help the Reflecting Pool absorb more heat. Higher temperatures encourage algae growth by allowing their metabolism to go into overdrive.
Summer temperatures in DC don’t help. Temperatures reached up to 95 degrees in the city this week. issuing a heat alarm.
This combination likely accounts for the overgrowth, turning the water surface an opaque green and preventing viewers from seeing the concrete pool’s new shade of blue.
Algae are important and beneficial organisms when the ecosystem is in balance. They form the basis of the aquatic food chain, fed by herbivores of all shapes and sizes, including shrimp and juvenile fish, which in turn feed organisms higher up the food chain. Single-celled organisms use the power of the sun to produce energy through photosynthesis, much like the houseplants on your balcony.
As part of combating algae in the Reflecting Pool, National Park Service workers were seen pouring gallons of hydrogen peroxide, a chemical commonly used in pool maintenance.
The Department of Internal Affairs also uses “high-tech nanobubble ozone technology” to destroy algal cells.
Ozone—yes, the same irritant in smoke—is a gas composed of three oxygen molecules, and the small size of the bubbles allows the most of the gas to be transferred into the water, where it can irritate our lungs as well as damage algae cells.
But this only treats the symptoms. In general, ozone nanobubbles are effective as a temporary solution against algal blooms. Longer-term fixes need to address the reasons that make the Reflecting Pool so ideal for algae, such as its depth, darker color, and nitrogen and phosphorus input.
In California, ozone nanobubbles were also used in a project to improve water quality in the Tijuana River. The 120-mile river, which flows near the border of northern Mexico and Southern California, was the site of a pilot study in 2025. The U.S. division of the International Boundary and Water Commission reported that nanobubbles have decreased.odor and bacteria,” but the project ended ahead of time After a flood, some of the tools were washed into the river.
