Anchor: They could not travel upriver because several sets of cataracts blocked passage and they did not know that the waters traveled from the heartland of Africa.
Entailed: Cataracts block travel up the river.  
Contradiction: The river has no cataracts, so travel up the river is easy.  
Contradiction: They had no difficulty travelling upriver, as there were no cataracts in the area. 
Contradiction: A person watching TV.
Contradiction: A man is climbing outdoors.
Contradiction: People are relaxing on the beach.