Cargo ships take on ballast water to stay stable at sea, then dump it in a different port thousands of miles away, along with whatever organisms were living in it. Invaders From the Sea, a BBC Wildvision production made for the International Maritime Organization, tracks how that routine practice has been moving toxic algae, bacteria, and small marine animals between coastlines and letting them establish themselves as invasive species far from home. The film lays out the ecological and economic damage this causes, from fisheries to coastal industries, and follows the response: GloBallast, a joint program of the Global Environment Facility, the United Nations Development Programme, and the IMO, built to coordinate ballast water management across the shipping industry worldwide. It is a plain account of an obscure but global problem, more focused on the mechanics of the threat and the international effort to regulate it than on any single location or case.