Solver pursuing Boatman up marshy creek (5)
I believe the answer is:
bayou
'marshy creek' is the definition.
'bayou' can be an answer for 'creek' (thesaurus). I'm not certain of the 'marshy' bit.
'solver pursuing boatman up' is the wordplay.
'solver' becomes 'you' (the person solving the clue!).
'pursuing' means one lot of letters go next to another.
'boatman' becomes 'ab' (abbreviation for able seaman).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'ab' written backwards gives 'ba'.
'you' after 'ba' is 'BAYOU'.
Can you help me to learn more?
(Other definitions for bayou that I've seen before include "US marshy delta, eg Mississippi" , "Swampy area" , "Watery area (US)" , "US marshland" , "Marshy outlet" .)