The ocean is the largest of the bodies of water on earth. Because of the presence of salt the biology and geology is different from a lake or other large body of water. Oceans cover more than 70% of all of earth's water and contain about 97% of the water. Harbors are located on the shoreline of an ocean, usually protected by landforms. Harbors provide an area for large vessels to dock, loading and unloading freight and passengers. Harbors may be naturally deep enough or have been created with human involvement.