A watershed: (definition by Wikipedia) In the technical sense, in the United States and Canada, the term "watershed" is often used to mean a drainage basin or catchment area. Watersheds drain into other watersheds in a hierarchical form, larger ones breaking into smaller ones or sub-watersheds with the topography determining where the water flows.
The Malibu Chapter of the Surfrider Foundation's Grant Neie, RN & Enviro Commitee Chair shows young surfing champ, Zander Hartman, the troubled sources of pollution that end up at world famous Malibu Surfrider Beach and in this particular scene, he describes a watershed, which is graphically illustrated.
The Flipside of Malibu is presented by the Malibu Chapter of the Surfrider Foundation. Flipside stars Grant Neie, Zander Hartman and Josh Samuel. It dramatizes the UCLA 2000 Study of pollution in the lower Malibu Creek, Floodplain, Wetland, lagoon and surfzone area in a 23 minute docudrama written by Grant Neie, Produced and Directed by Bob Purvey.