Cross Irish river, date swimming on it (9)
I believe the answer is:
irritated
'cross' is the definition.
(I've seen this before)
'irish river date swimming on it' is the wordplay.
'irish' becomes 'IR' (abbreviation).
'river' becomes 'r' (abbreviation).
'swimming' is an anagram indicator (letters swim around into a new order).
'on' is an insertion indicator (as in clothing 'on' a person).
'date' is an anagram of 'ated'.
'ated' enclosing 'it' is 'itated'.
'ir'+'r'+'itated'='IRRITATED'
(Other definitions for irritated that I've seen before include "Annoyed" , "Vexed" , "Cross" , "Irked" , "Ratty" .)