Thug crossing river channel (6)
I believe the answer is:
trough
'channel' is the definition.
(trough is a kind of channel)
'thug crossing river' is the wordplay.
'thug' becomes 'tough' ('tough' can be a synonym of 'thug').
'crossing' means one lot of letters goes inside another.
'river' becomes 'r'.
'tough' going around 'r' is 'TROUGH'.
(Other definitions for trough that I've seen before include "Farm food container" , "Pigswill container" , "Hollow between wave crests" , "Depression - animal food holder" , "Long container for animal feed" .)