impassable
adjective /ɪmˈpɑːsəbl/
  /ɪmˈpæsəbl/
 - (of a road, an area, etc.) impossible to travel on or through, especially because it is in bad condition or it has been blocked by something
- The mountain roads are totally impassable to cars in winter.
 - After the storm, many roads were made impassable by fallen trees.
 - The river formed an impassable barrier for migrating animals.
 - The river’s broad mudflats were thought completely impassable.
 
Oxford Collocations Dictionaryverbs- be
 - become
 - remain
 - …
 
- completely
 - totally
 - almost
 - …
 
Word Originmid 16th cent.: perhaps via French.