Pigs or snakes crossing river (5)
I believe the answer is:
boars
'pigs' is the definition.
(male pigs)
'snakes crossing river' is the wordplay.
'snakes' becomes 'boas' (boa is a kind of snake).
'crossing' is an insertion indicator (to cross can mean to go over or around).
'river' becomes 'r' (abbreviation for river).
'boas' enclosing 'r' is 'BOARS'.
'or' is the link.
(Other definitions for boars that I've seen before include "Male badgers" , "Wild swine" , "Male or wild pigs" .)