The Lincoln Memorial Reflecting Pool in Washington, D.C., is once again facing issues with persistent algae growth shortly after reopening following a major renovation. The pool, which holds approximately 6.7 million gallons of water and varies in depth from 18 to 30 inches, underwent a $14 million refurbishment ordered by former President Donald Trump. The project included sealing the concrete bottom with a blue coating described as “American flag blue.”

Despite the recent work, the green algae that has long troubled the reflecting pool quickly returned after it was refilled. The National Park Service (NPS) attributed the algae resurgence to dormant algae remaining in the pool’s filtration pipes during the refurbishment period. According to an NPS spokesperson, the algae bloom is part of a normal startup process following pool maintenance.

Officials stated that cleanup measures are underway, including the use of nanobubbler technology intended to keep the water clear and algae-free. Nanobubblers generate tiny oxygen bubbles that increase water circulation and oxygen levels, which can inhibit algae growth.

However, observers at the site have noted that the green, murky appearance of the reflecting pool persisted over the weekend despite these efforts. The recurring nature of the algae problem has raised questions about the effectiveness of the recent renovation in addressing long-standing water quality concerns.

The reflecting pool, constructed in the early 1920s, has faced algae challenges for decades due to its shallow depth and large surface area, which can promote algae proliferation, especially in warmer months. The NPS continues to monitor the situation and is implementing strategies to improve water clarity in the historic landmark’s basin.