In the early 1980s, a scientist invented a machine that could naturally filter out pollution from rivers, lakes, and other bodies of water. So, why isn't it everywhere today? In this episode, we explore the secret behind this powerful green technology (spoiler alert: it's algae!) and track its journey from a coral reef in the Caribbean to the basement of the National Museum of Natural History in Washington, D.C., and finally a port in Baltimore, where it is now being used to clean up one of the region's most polluted waterways.