Investigate about harbour (6)
I believe the answer is:
report
'investigate' is the definition.
(thesaurus)
'about harbour' is the wordplay.
'about' becomes 're' (regarding).
'harbour' becomes 'port' (I've seen this before).
're'+'port'='REPORT'
(Other definitions for report that I've seen before include "result of firing?" , "Make a complaint about (someone)" , "Sudden noise; account of progress" , "Make a formal complaint" , "Noise - information" .)