what happens to contour lines when they cross a stream.?

Answer 1

From the site linked below:

"Since streams are found in local topographic lows, the contour lines double back on themselves forming a "V" shape pattern. "

Check the site for more information.

http://raider.muc.edu/~mcnaugma/Topographic%20Maps/streams_and_stream_valleys.htm

Answer 2

It depends on whether they can swim or not!