#bed.natural_depression__bottom  a depression forming the ground under a body of water; "he searched for treasure on the ocean bed"
  supertype:  #natural_depression__naturaldepression__depression  a sunken or depressed geological formation
  subtype:  #lake_bed__lake_bottom  the bottom of a lake
  subtype:  #ocean_floor__oceanfloor__ocean_bottom__oceanbottom__seabed__sea_bottom__seabottom__Davy_Jones's_locker__Davy_Jones  the bottom of a sea or ocean
     subtype:  #abyssal_zone__abyssalzone  the deep sea (2000 meters or more) where there is no light
     subtype:  #continental_shelf__continentalshelf  the relatively shallow (up to 200 meters) seabed surrounding a continent
     subtype:  #continental_slope__continentalslope__bathyal_zone__bathyalzone__bathyal_district__bathyaldistrict  the steep descent of the seabed from the continental shelf to the abyssal zone
  subtype:  #riverbed__river_bottom__riverbottom  a channel occupied (or formerly occupied) by a river
  subtype:  #streambed__creek_bed__creekbed  a channel occupied (or formerly occupied) by a stream
     subtype:  #dry_wash__drywash__wash  (western United States) the dry bed of an intermittent stream (as at the bottom of a canyon)

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