Vexed witness reported dangerous swimming conditions (5,3)
I believe the answer is:
cross sea
'dangerous swimming conditions' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'vexed witness reported' is the wordplay.
'vexed' becomes 'cross' (both can mean angry).
'witness' becomes 'see' (synonyms).
'reported' indicates a 'sounds like' (homophone) clue.
'see' is a homophone of 'sea'.
'cross'+'sea'='CROSS SEA'
Can you help me to learn more?
(Another definition for cross sea that I've seen is " Ocean moving at an angle to the wind direction".)