Lincoln Memorial Reflecting Pool Turns Green Days After Refill

The Lincoln Memorial Reflecting Pool has turned green days after being refilled following a renovation that applied a dark blue coating. The overhaul was ordered as part of work on the National Mall ahead of the U.S. 250th anniversary. Federal records show contracts reached roughly $14 million, compared with earlier estimates of $1.5 million to $2 million.

The project used a no-bid contract and has prompted a lawsuit from preservation group The Cultural Landscape Foundation, which argues the changes bypassed required historic review.

Background on the Pool The reflecting pool stretches more than 2,000 feet between the Lincoln Memorial and the Washington Monument and has been in place since 1923. Algae blooms have occurred before, including after a $34 million renovation in 2012 when the water turned green within weeks.

An Interior Department spokesperson told Politico the current algae is residual after supply lines sat dormant for eight weeks during construction.

Silkina, an algal biotechnology expert at Swansea University, said darker surfaces absorb more sunlight and can raise water temperatures, though she noted nutrient levels, water residence time, and species composition are usually more important factors.

Warm temperatures, strong sunlight, and still conditions also favor algae growth in shallow water. Silkina added that continuous water circulation can reduce bloom development by preventing algae from accumulating in one place. The green color results from chlorophyll in the algae, which can multiply quickly under favorable conditions.

Silkina said populations can double within hours to days and visible blooms can appear within several days to two weeks. Some social media users have speculated without evidence that the pool was sabotaged. There is no public evidence to support those claims, and officials have not indicated any foul play.