Ahead of the 250th anniversary of the Declaration of Independence in the U.S., an ozone nanobubble system has been used to keep the Lincoln Memorial Reflecting Pool clear. Months before the celebrations, a massive cleanup of the pool had taken place, but despite this, an algae bloom had turned the water bright green. To deal with this, a US$1.7 million (£1.27 million) ozone "nanobubbler" injected microscopic bubbles into the pool.