mid ‧ stream /ˌmɪdˈstriːm◂/ BrE AmE noun [uncountable]
1 . in midstream when something has started and is still happening:
They had to drop the experiment in midstream.
He interrupted the official in midstream (=while the official was still speaking) .
2 . the middle part of a river
in midstream
The boat had anchored in midstream.
—midstream adverb