Overwhelm, swamp (8)
I believe the answer is:
inundate
I believe this clue is a double definition.
'overwhelm' is the first definition.
(inundate can mean to overwhelm or overload)
'swamp' is the second definition.
(synonyms)
(Other definitions for inundate that I've seen before include "be overwhelming" , "Overwhelm (as if) with water" , "'Flood, swamp (8)'" , "Flood, cover with water" , "Overwhelm with things to be done" .)