Trash, packaging, and waste improperly disposed on land are washing into rivers, streams, lakes and creeks, and from there to the ocean. This is estimated to account for 80% of the marine debris in the oceans.
Rivers typically begin at mountaintops where melting snow and ice create streams, which often merge to form larger rivers. As water flows from high elevations to low elevations, it carves deep, V-shaped valleys in the mountains, transitions to wider valleys with meandering streams, and eventually reaches floodplains where it may split into channels and form deltas before draining into the ocean. A watershed, or drainage basin, is the land area that collects rainfall and snowmelt, directing it into rivers, streams, and ultimately to larger bodies of water like bays and oceans.