Bubbling up by river in African country, is maelstrom (9)
I believe the answer is:
charybdis
'maelstrom' is the definition.
(whirlpool monster in Greek myth)
'bubbling up by river in african country is' is the wordplay.
'bubbling up' shows that the letters should be reversed in order (in a down clue, letters go up).
'river' becomes 'r' (abbreviation for river).
'in' indicates putting letters inside.
'african country' becomes 'Chad' (country in Africa).
'by'+'r'='byr'
'byr' backwards is 'ryb'.
'ryb' put within 'chad' is 'charybd'.
'charybd'+'is'='CHARYBDIS'
(Other definitions for charybdis that I've seen before include "Scylla's counterpart" , "Mythical whirlpool" , "Whirlpool, across from 14" , "Whirlpool opposite Scylla" , "monster" .)