Discover how a ''killer algae'' is causing ecological disaster around the world. ''It’s like out of a horror movie... but it’s real,'' claims one marine biologist about the innocent-looking algae that is actually threatening ecosystems from the Mediterranean Sea to the California coast. Like the eerie start of a chilling science-fiction film, the first small patch of this mysterious seaweed was discovered off the coast of Monaco in 1989. Today, the noxious weed covers vast areas around the globe, causing many marine experts to dub it an ecological disaster. NOVA tracks the past, present, and future of this killer algae, exploring how a supposedly harmless plant once bred to decorate fish tanks and museum aquariums escaped into the Mediterranean and became the monster that now chokes out indigenous sea-life whereever it spreads. Meet the biologist who was first to sound the alarm and discover the shocking story of how this green monster was first released into the sea. Learn how this algae now spreads unchallenged on the sea floor. And see how one possible solution is stirring debate and igniting controversy.