#water_system__watersystem  a river and all of its tributaries
  supertype:  #system  a group of independent but interrelated elements comprising a unified whole; "a vast system of production and distribution and consumption keep the country going"
  part:  #river  a large natural stream of water (larger than a creek); "the river was navigable for 50 miles"
     part:  #estuary  the wide part of a river where it nears the sea; fresh and salt water mix
     part:  #rapid  a part of a river where the current is very fast
     part:  #waterfall__falls__fall__cascade__cataract  a steep descent of the water of a river

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