Sadly untrained, not seeing river flood (8)
I believe the answer is:
inundate
'flood' is the definition.
('inundate' can be a synonym of 'flood')
'sadly untrained not seeing river' is the wordplay.
'sadly' is an anagram indicator.
'not' indicates named letters should be taken away.
'seeing river' becomes 'r'.
'untrained' with 'r' taken away is 'untained'.
'untained' anagrammed gives 'INUNDATE'.
(Other definitions for inundate that I've seen before include "Overwhelm with things to be done" , "Flood, cover with water" , "Flood (a place)" , "Overrun" , "'Flood, swamp (8)'" .)