midstream
noun /ˌmɪdˈstriːm/
  /ˌmɪdˈstriːm/
 [uncountable]Idioms - the middle part of a river, stream, etc.
- We anchored in midstream.
 - The boat drifted out into midstream.
 
 
Idioms 
change horses in midstream 
- to change to a different or new activity while you are in the middle of something else; to change from supporting one person or thing to another                                     
 
(in) midstream 
- in the middle of doing something; while something is still happening
- Their conversation was interrupted in midstream by the baby crying.