Don't go in small river (4)
I believe the answer is:
stay
'don't go' is the definition.
(I've seen this in another clue)
'small river' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'river' becomes 'tay' (River Tay).
's'+'tay'='STAY'
'in' is the link.
(Other definitions for stay that I've seen before include "Remain; steady" , "Supporting rope; remain" , "Stop; support" , "Abide" , "Supporting rope or wire" .)