Algae bloom turns newly painted Reflecting Pool green despite renovation efforts

The Reflecting Pool on the National Mall, recently renovated with a new dark-blue coating, has developed a green hue as algae proliferated after a period of hot weather. The Interior Department said the National Park Service is treating the water with nanobubble ozone technology and hydrogen peroxide, which it described as having no harmful side effects to marine life or the environment.

The pool’s shallow, sun-exposed design makes it susceptible to algal blooms, which are fueled by nutrients such as nitrogen and phosphorus from wildlife waste and runoff. The Centers for Disease Control and Prevention notes that these conditions can accelerate growth.

President Donald Trump previously highlighted the repainting, calling the color “American flag blue” and stating the project cost about $10 million. Interior Secretary Doug Burgum, who has been referred to as Trump’s “pool guy,” defended the work, saying the agency is maintaining the “beautifully completed” pool, in contrast to previous administrations.

The renovation, carried out through a no-bid contract valued at more than $13 million, faced legal challenges from the Cultural Landscape Foundation, which sued to block the repainting. During a congressional hearing, Burgum affirmed confidence that required bidding rules were followed.

The change in water color comes as the nation prepares for its 250th anniversary celebrations, during which the Reflecting Pool is expected to feature prominently in planned events.