Physical Map of the USA

Look at the map of the US below.  Can you find some blue, squiggly lines which represent rivers? 

Are there any which go all the way from the east coast to the west coast?  No, there are not.

Many explorers thought and hoped there was a river or waterway across North America. 

If they could find one, it would decrease the length of their trip to Asia.  They were going to Asia to trade for spices.

We know now there is no such waterway, but those explorers called what they were looking for the Northwest Passage.