American flag blue to pipes: 4 theories why Lincoln Memorial Pool is now green

Key Points:

• The Lincoln Memorial Reflecting Pool underwent a $14 million renovation to deepen its "American flag blue" color and seal leaks, but soon after refilling, algae blooms caused the water to appear green, raising concerns about the redesign's impact on algae growth.
• Experts suggest multiple factors contribute to the algae blooms, including residual algae from construction, the darker blue coating absorbing more heat and sunlight, warm weather conditions, and possible issues with water circulation and infrastructure beneath the pool.
• Algae growth is accelerated by higher water temperatures and sunlight in shallow, slow-moving water, with nutrients like nitrogen and phosphorus also playing a key role; the green color results from chlorophyll in the algae dominating the water's appearance.
• The renovation contract was awarded without a competitive bidding process, prompting criticism and a lawsuit from preservation groups citing lack of historic review, while some social media claims of sabotage lack any evidence.
• Similar algae issues have occurred after previous renovations, highlighting the ongoing challenge of controlling algae blooms in the reflecting pool despite efforts to improve its condition.